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Sendmux

Sendmux Email Inbox API + Sending

Official
by Sendmux

Get Message

mailbox_get_message
Read-onlyIdempotent

Retrieve a specific email message by ID, returning its summary or detail fields. Use when you need message metadata without the full body content.

Instructions

Use this to fetch one message summary or detail by message_id. Use mailbox_list_body or mailbox_list_content when the body content is required.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
mailbox_idNoMailbox public ID to target when the credential grants access to more than one mailbox. Omit when the credential is scoped to exactly one mailbox.
message_idYesMessage ID.
If-None-MatchNoWeak ETag from a previous response. Returns 304 when unchanged.

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
resultYes

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv1.0.14
    • changedOutput schema / properties / result / allOf
      Previous value: -[
      -  {
      -    "properties": {
      -      "meta": {
      -        "additionalProperties": {},
      -        "properties": {},
      -        "type": "object"
      -      },
      -      "ok": {
      -        "enum": [
      -          true
      -        ],
      -        "type": "boolean"
      -      }
      -    },
      -    "required": [
      -      "ok",
      -      "meta"
      -    ],
      -    "type": "object"
      -  },
      -  {
      -    "properties": {
      -      "data": {
      -        "additionalProperties": false,
      -        "properties": {
      -          "attachments": {
      -            "description": "Attachment metadata for this message. Each item includes a short-lived `download_url`; if it expires, fetch message metadata again.",
      -            "items": {
      -              "additionalProperties": false,
      -              "properties": {
      -                "content_id": {
      -                  "description": "Content ID for inline attachments, when present.",
      -                  "type": [
      -                    "string",
      -                    "null"
      -                  ]
      -                },
      -                "content_type": {
      -                  "example": "application/pdf",
      -                  "type": "string"
      -                },
      -                "disposition": {
      -                  "example": "attachment",
      -                  "type": [
      -                    "string",
      -                    "null"
      -                  ]
      -                },
      -                "download_url": {
      -                  "description": "Short-lived URL for this exact attachment. Fetch it promptly; if it expires, call the message or attachment metadata endpoint again to receive a fresh URL.",
      -                  "example": "https://app.sendmux.ai/api/v1/mailbox/messages/msg_123/attachment-downloads/attref_abc123?download_token=...",
      -                  "type": "string"
      -                },
      -                "filename": {
      -                  "example": "invoice.pdf",
      -                  "type": [
      -                    "string",
      -                    "null"
      -                  ]
      -                },
      -                "id": {
      -                  "description": "Attachment blob ID.",
      -                  "type": "string"
      -                },
      -                "size_bytes": {
      -                  "example": 12345,
      -                  "type": [
      -                    "integer",
      -                    "null"
      -                  ]
      -                }
      -              },
      -              "required": [
      -                "id",
      -                "filename",
      -                "content_type",
      -                "size_bytes",
      -                "disposition",
      -                "content_id"
      -              ],
      -              "type": "object"
      -            },
      -            "type": "array"
      -          },
      -          "bcc": {
      -            "items": {
      -              "additionalProperties": false,
      -              "properties": {
      -                "email": {
      -                  "example": "agent@example.com",
      -                  "format": "email",
      -                  "type": "string"
      -                },
      -                "name": {
      -                  "example": "Support",
      -                  "type": [
      -                    "string",
      -                    "null"
      -                  ]
      -                }
      -              },
      -              "required": [
      -                "email",
      -                "name"
      -              ],
      -              "type": "object"
      -            },
      -            "type": "array"
      -          },
      -          "cc": {
      -            "items": {
      -              "additionalProperties": false,
      -              "properties": {
      -                "email": {
      -                  "example": "agent@example.com",
      -                  "format": "email",
      -                  "type": "string"
      -                },
      -                "name": {
      -                  "example": "Support",
      -                  "type": [
      -                    "string",
      -                    "null"
      -                  ]
      -                }
      -              },
      -              "required": [
      -                "email",
      -                "name"
      -              ],
      -              "type": "object"
      -            },
      -            "type": "array"
      -          },
      -          "flags": {
      -            "additionalProperties": false,
      -            "properties": {
      -              "answered": {
      -                "type": "boolean"
      -              },
      -              "draft": {
      -                "type": "boolean"
      -              },
      -              "flagged": {
      -                "type": "boolean"
      -              },
      -              "seen": {
      -                "type": "boolean"
      -              }
      -            },
      -            "required": [
      -              "seen",
      -              "flagged",
      -              "draft",
      -              "answered"
      -            ],
      -            "type": "object"
      -          },
      -          "folder_ids": {
      -            "items": {
      -              "type": "string"
      -            },
      -            "type": "array"
      -          },
      -          "from": {
      -            "allOf": [
      -              {
      -                "additionalProperties": false,
      -                "properties": {
      -                  "email": {
      -                    "example": "agent@example.com",
      -                    "format": "email",
      -                    "type": "string"
      -                  },
      -                  "name": {
      -                    "example": "Support",
      -                    "type": [
      -                      "string",
      -                      "null"
      -                    ]
      -                  }
      -                },
      -                "required": [
      -                  "email",
      -                  "name"
      -                ],
      -                "type": "object"
      -              },
      -              {
      -                "type": [
      -                  "object",
      -                  "null"
      -                ]
      -              }
      -            ]
      -          },
      -          "has_attachments": {
      -            "type": "boolean"
      -          },
      -          "html_body": {
      -            "type": [
      -              "string",
      -              "null"
      -            ]
      -          },
      -          "id": {
      -            "description": "Message ID",
      -            "type": "string"
      -          },
      -          "keywords": {
      -            "description": "Active message keywords, including system flags and custom labels.",
      -            "example": [
      -              "$seen",
      -              "$flagged",
      -              "agent_triaged"
      -            ],
      -            "items": {
      -              "type": "string"
      -            },
      -            "type": "array"
      -          },
      -          "preview": {
      -            "type": [
      -              "string",
      -              "null"
      -            ]
      -          },
      -          "received_at": {
      -            "type": [
      -              "string",
      -              "null"
      -            ]
      -          },
      -          "sent_at": {
      -            "type": [
      -              "string",
      -              "null"
      -            ]
      -          },
      -          "size_bytes": {
      -            "type": [
      -              "integer",
      -              "null"
      -            ]
      -          },
      -          "subject": {
      -            "type": [
      -              "string",
      -              "null"
      -            ]
      -          },
      -          "text_body": {
      -            "type": [
      -              "string",
      -              "null"
      -            ]
      -          },
      -          "thread_id": {
      -            "type": [
      -              "string",
      -              "null"
      -            ]
      -          },
      -          "to": {
      -            "items": {
      -              "additionalProperties": false,
      -              "properties": {
      -                "email": {
      -                  "example": "agent@example.com",
      -                  "format": "email",
      -                  "type": "string"
      -                },
      -                "name": {
      -                  "example": "Support",
      -                  "type": [
      -                    "string",
      -                    "null"
      -                  ]
      -                }
      -              },
      -              "required": [
      -                "email",
      -                "name"
      -              ],
      -              "type": "object"
      -            },
      -            "type": "array"
      -          }
      -        },
      -        "required": [
      -          "id",
      -          "thread_id",
      -          "folder_ids",
      -          "subject",
      -          "preview",
      -          "from",
      -          "to",
      -          "cc",
      -          "bcc",
      -          "received_at",
      -          "sent_at",
      -          "size_bytes",
      -          "has_attachments",
      -          "keywords",
      -          "flags",
      -          "text_body",
      -          "html_body"
      -        ],
      -        "type": "object"
      -      },
      -      "meta": {
      -        "additionalProperties": false,
      -        "properties": {
      -          "request_id": {
      -            "example": "req_clxxxxxxxxxxxxxxxxxxxxxxxxx",
      -            "type": "string"
      -          }
      -        },
      -        "required": [
      -          "request_id"
      -        ],
      -        "type": "object"
      -      }
      -    },
      -    "required": [
      -      "data"
      -    ],
      -    "type": "object"
      -  }
      -]New value: +[
      +  {
      +    "properties": {
      +      "meta": {
      +        "additionalProperties": {},
      +        "properties": {},
      +        "type": "object"
      +      },
      +      "ok": {
      +        "enum": [
      +          true
      +        ],
      +        "type": "boolean"
      +      }
      +    },
      +    "required": [
      +      "ok",
      +      "meta"
      +    ],
      +    "type": "object"
      +  },
      +  {
      +    "properties": {
      +      "data": {
      +        "additionalProperties": false,
      +        "properties": {
      +          "attachments": {
      +            "description": "Attachment metadata for this message. Each item includes a short-lived `download_url`; if it expires, fetch message metadata again.",
      +            "items": {
      +              "additionalProperties": false,
      +              "properties": {
      +                "content_id": {
      +                  "description": "Content ID for inline attachments, when present.",
      +                  "type": [
      +                    "string",
      +                    "null"
      +                  ]
      +                },
      +                "content_type": {
      +                  "example": "application/pdf",
      +                  "type": "string"
      +                },
      +                "disposition": {
      +                  "example": "attachment",
      +                  "type": [
      +                    "string",
      +                    "null"
      +                  ]
      +                },
      +                "download_url": {
      +                  "description": "Short-lived URL for this exact attachment. Fetch it promptly; if it expires, call the message or attachment metadata endpoint again to receive a fresh URL.",
      +                  "example": "https://app.sendmux.ai/api/v1/mailbox/messages/msg_123/attachment-downloads/attref_abc123?download_token=...",
      +                  "type": "string"
      +                },
      +                "filename": {
      +                  "example": "invoice.pdf",
      +                  "type": [
      +                    "string",
      +                    "null"
      +                  ]
      +                },
      +                "id": {
      +                  "description": "Attachment blob ID.",
      +                  "type": "string"
      +                },
      +                "size_bytes": {
      +                  "example": 12345,
      +                  "type": [
      +                    "integer",
      +                    "null"
      +                  ]
      +                }
      +              },
      +              "required": [
      +                "id",
      +                "filename",
      +                "content_type",
      +                "size_bytes",
      +                "disposition",
      +                "content_id"
      +              ],
      +              "type": "object"
      +            },
      +            "type": "array"
      +          },
      +          "bcc": {
      +            "items": {
      +              "additionalProperties": false,
      +              "properties": {
      +                "email": {
      +                  "example": "agent@example.com",
      +                  "format": "email",
      +                  "type": "string"
      +                },
      +                "name": {
      +                  "example": "Support",
      +                  "type": [
      +                    "string",
      +                    "null"
      +                  ]
      +                }
      +              },
      +              "required": [
      +                "email",
      +                "name"
      +              ],
      +              "type": "object"
      +            },
      +            "type": "array"
      +          },
      +          "cc": {
      +            "items": {
      +              "additionalProperties": false,
      +              "properties": {
      +                "email": {
      +                  "example": "agent@example.com",
      +                  "format": "email",
      +                  "type": "string"
      +                },
      +                "name": {
      +                  "example": "Support",
      +                  "type": [
      +                    "string",
      +                    "null"
      +                  ]
      +                }
      +              },
      +              "required": [
      +                "email",
      +                "name"
      +              ],
      +              "type": "object"
      +            },
      +            "type": "array"
      +          },
      +          "flags": {
      +            "additionalProperties": false,
      +            "properties": {
      +              "answered": {
      +                "type": "boolean"
      +              },
      +              "draft": {
      +                "type": "boolean"
      +              },
      +              "flagged": {
      +                "type": "boolean"
      +              },
      +              "seen": {
      +                "type": "boolean"
      +              }
      +            },
      +            "required": [
      +              "seen",
      +              "flagged",
      +              "draft",
      +              "answered"
      +            ],
      +            "type": "object"
      +          },
      +          "folder_ids": {
      +            "items": {
      +              "type": "string"
      +            },
      +            "type": "array"
      +          },
      +          "from": {
      +            "anyOf": [
      +              {
      +                "additionalProperties": false,
      +                "properties": {
      +                  "email": {
      +                    "example": "agent@example.com",
      +                    "format": "email",
      +                    "type": "string"
      +                  },
      +                  "name": {
      +                    "example": "Support",
      +                    "type": [
      +                      "string",
      +                      "null"
      +                    ]
      +                  }
      +                },
      +                "required": [
      +                  "email",
      +                  "name"
      +                ],
      +                "type": "object"
      +              },
      +              {
      +                "type": "null"
      +              }
      +            ]
      +          },
      +          "has_attachments": {
      +            "type": "boolean"
      +          },
      +          "html_body": {
      +            "type": [
      +              "string",
      +              "null"
      +            ]
      +          },
      +          "id": {
      +            "description": "Message ID",
      +            "type": "string"
      +          },
      +          "in_reply_to": {
      +            "description": "`In-Reply-To` header values, with the surrounding angle brackets removed — the message this one replies to. Empty when the message is not a reply.",
      +            "example": [
      +              "20260918.0009@example.com"
      +            ],
      +            "items": {
      +              "type": "string"
      +            },
      +            "type": "array"
      +          },
      +          "keywords": {
      +            "description": "Active message keywords, including system flags and custom labels.",
      +            "example": [
      +              "$seen",
      +              "$flagged",
      +              "agent_triaged"
      +            ],
      +            "items": {
      +              "type": "string"
      +            },
      +            "type": "array"
      +          },
      +          "message_id": {
      +            "description": "`Message-ID` header values for this message, with the surrounding angle brackets removed. Empty when the message carries no `Message-ID`.",
      +            "example": [
      +              "20260919.0001@example.com"
      +            ],
      +            "items": {
      +              "type": "string"
      +            },
      +            "type": "array"
      +          },
      +          "preview": {
      +            "type": [
      +              "string",
      +              "null"
      +            ]
      +          },
      +          "received_at": {
      +            "type": [
      +              "string",
      +              "null"
      +            ]
      +          },
      +          "references": {
      +            "description": "`References` header values, with the surrounding angle brackets removed — the ancestor chain of this message, oldest first. Empty when the message starts a conversation.",
      +            "example": [
      +              "20260917.0001@example.com",
      +              "20260918.0009@example.com"
      +            ],
      +            "items": {
      +              "type": "string"
      +            },
      +            "type": "array"
      +          },
      +          "reply_to": {
      +            "description": "`Reply-To` addresses. Address replies here rather than to `from` whenever this is non-empty. Empty when the message carries no `Reply-To`.",
      +            "items": {
      +              "additionalProperties": false,
      +              "properties": {
      +                "email": {
      +                  "example": "agent@example.com",
      +                  "format": "email",
      +                  "type": "string"
      +                },
      +                "name": {
      +                  "example": "Support",
      +                  "type": [
      +                    "string",
      +                    "null"
      +                  ]
      +                }
      +              },
      +              "required": [
      +                "email",
      +                "name"
      +              ],
      +              "type": "object"
      +            },
      +            "type": "array"
      +          },
      +          "sent_at": {
      +            "type": [
      +              "string",
      +              "null"
      +            ]
      +          },
      +          "size_bytes": {
      +            "type": [
      +              "integer",
      +              "null"
      +            ]
      +          },
      +          "subject": {
      +            "type": [
      +              "string",
      +              "null"
      +            ]
      +          },
      +          "text_body": {
      +            "type": [
      +              "string",
      +              "null"
      +            ]
      +          },
      +          "thread_id": {
      +            "type": [
      +              "string",
      +              "null"
      +            ]
      +          },
      +          "to": {
      +            "items": {
      +              "additionalProperties": false,
      +              "properties": {
      +                "email": {
      +                  "example": "agent@example.com",
      +                  "format": "email",
      +                  "type": "string"
      +                },
      +                "name": {
      +                  "example": "Support",
      +                  "type": [
      +                    "string",
      +                    "null"
      +                  ]
      +                }
      +              },
      +              "required": [
      +                "email",
      +                "name"
      +              ],
      +              "type": "object"
      +            },
      +            "type": "array"
      +          }
      +        },
      +        "required": [
      +          "id",
      +          "thread_id",
      +          "folder_ids",
      +          "subject",
      +          "preview",
      +          "from",
      +          "to",
      +          "cc",
      +          "bcc",
      +          "received_at",
      +          "sent_at",
      +          "size_bytes",
      +          "has_attachments",
      +          "keywords",
      +          "flags",
      +          "text_body",
      +          "html_body",
      +          "message_id",
      +          "in_reply_to",
      +          "references",
      +          "reply_to"
      +        ],
      +        "type": "object"
      +      },
      +      "meta": {
      +        "additionalProperties": false,
      +        "properties": {
      +          "request_id": {
      +            "example": "req_clxxxxxxxxxxxxxxxxxxxxxxxxx",
      +            "type": "string"
      +          }
      +        },
      +        "required": [
      +          "request_id"
      +        ],
      +        "type": "object"
      +      }
      +    },
      +    "required": [
      +      "data"
      +    ],
      +    "type": "object"
      +  }
      +]
  2. Changed1 schema field changedv1.0.12
    • changedOutput schema / properties / result / allOf
      Previous value: -[
      -  {
      -    "properties": {
      -      "meta": {
      -        "additionalProperties": {},
      -        "properties": {},
      -        "type": "object"
      -      },
      -      "ok": {
      -        "enum": [
      -          true
      -        ],
      -        "type": "boolean"
      -      }
      -    },
      -    "required": [
      -      "ok",
      -      "meta"
      -    ],
      -    "type": "object"
      -  },
      -  {
      -    "properties": {
      -      "data": {
      -        "allOf": [
      -          {
      -            "additionalProperties": false,
      -            "properties": {
      -              "attachments": {
      -                "description": "Attachment metadata for this message. Each item includes a short-lived `download_url`; if it expires, fetch message metadata again.",
      -                "items": {
      -                  "additionalProperties": false,
      -                  "properties": {
      -                    "content_id": {
      -                      "description": "Content ID for inline attachments, when present.",
      -                      "type": [
      -                        "string",
      -                        "null"
      -                      ]
      -                    },
      -                    "content_type": {
      -                      "example": "application/pdf",
      -                      "type": "string"
      -                    },
      -                    "disposition": {
      -                      "example": "attachment",
      -                      "type": [
      -                        "string",
      -                        "null"
      -                      ]
      -                    },
      -                    "download_url": {
      -                      "description": "Short-lived URL for this exact attachment. Fetch it promptly; if it expires, call the message or attachment metadata endpoint again to receive a fresh URL.",
      -                      "example": "https://app.sendmux.ai/api/v1/mailbox/messages/msg_123/attachment-downloads/attref_abc123?download_token=...",
      -                      "type": "string"
      -                    },
      -                    "filename": {
      -                      "example": "invoice.pdf",
      -                      "type": [
      -                        "string",
      -                        "null"
      -                      ]
      -                    },
      -                    "id": {
      -                      "description": "Attachment blob ID.",
      -                      "type": "string"
      -                    },
      -                    "size_bytes": {
      -                      "example": 12345,
      -                      "type": [
      -                        "integer",
      -                        "null"
      -                      ]
      -                    }
      -                  },
      -                  "required": [
      -                    "id",
      -                    "filename",
      -                    "content_type",
      -                    "size_bytes",
      -                    "disposition",
      -                    "content_id"
      -                  ],
      -                  "type": "object"
      -                },
      -                "type": "array"
      -              },
      -              "bcc": {
      -                "items": {
      -                  "additionalProperties": false,
      -                  "properties": {
      -                    "email": {
      -                      "example": "agent@example.com",
      -                      "format": "email",
      -                      "type": "string"
      -                    },
      -                    "name": {
      -                      "example": "Support",
      -                      "type": [
      -                        "string",
      -                        "null"
      -                      ]
      -                    }
      -                  },
      -                  "required": [
      -                    "email",
      -                    "name"
      -                  ],
      -                  "type": "object"
      -                },
      -                "type": "array"
      -              },
      -              "cc": {
      -                "items": {
      -                  "additionalProperties": false,
      -                  "properties": {
      -                    "email": {
      -                      "example": "agent@example.com",
      -                      "format": "email",
      -                      "type": "string"
      -                    },
      -                    "name": {
      -                      "example": "Support",
      -                      "type": [
      -                        "string",
      -                        "null"
      -                      ]
      -                    }
      -                  },
      -                  "required": [
      -                    "email",
      -                    "name"
      -                  ],
      -                  "type": "object"
      -                },
      -                "type": "array"
      -              },
      -              "flags": {
      -                "additionalProperties": false,
      -                "properties": {
      -                  "answered": {
      -                    "type": "boolean"
      -                  },
      -                  "draft": {
      -                    "type": "boolean"
      -                  },
      -                  "flagged": {
      -                    "type": "boolean"
      -                  },
      -                  "seen": {
      -                    "type": "boolean"
      -                  }
      -                },
      -                "required": [
      -                  "seen",
      -                  "flagged",
      -                  "draft",
      -                  "answered"
      -                ],
      -                "type": "object"
      -              },
      -              "folder_ids": {
      -                "items": {
      -                  "type": "string"
      -                },
      -                "type": "array"
      -              },
      -              "from": {
      -                "allOf": [
      -                  {
      -                    "additionalProperties": false,
      -                    "properties": {
      -                      "email": {
      -                        "example": "agent@example.com",
      -                        "format": "email",
      -                        "type": "string"
      -                      },
      -                      "name": {
      -                        "example": "Support",
      -                        "type": [
      -                          "string",
      -                          "null"
      -                        ]
      -                      }
      -                    },
      -                    "required": [
      -                      "email",
      -                      "name"
      -                    ],
      -                    "type": "object"
      -                  },
      -                  {
      -                    "type": [
      -                      "object",
      -                      "null"
      -                    ]
      -                  }
      -                ]
      -              },
      -              "has_attachments": {
      -                "type": "boolean"
      -              },
      -              "id": {
      -                "description": "Message ID",
      -                "type": "string"
      -              },
      -              "keywords": {
      -                "description": "Active message keywords, including system flags and custom labels.",
      -                "example": [
      -                  "$seen",
      -                  "$flagged",
      -                  "agent_triaged"
      -                ],
      -                "items": {
      -                  "type": "string"
      -                },
      -                "type": "array"
      -              },
      -              "preview": {
      -                "type": [
      -                  "string",
      -                  "null"
      -                ]
      -              },
      -              "received_at": {
      -                "type": [
      -                  "string",
      -                  "null"
      -                ]
      -              },
      -              "sent_at": {
      -                "type": [
      -                  "string",
      -                  "null"
      -                ]
      -              },
      -              "size_bytes": {
      -                "type": [
      -                  "integer",
      -                  "null"
      -                ]
      -              },
      -              "subject": {
      -                "type": [
      -                  "string",
      -                  "null"
      -                ]
      -              },
      -              "thread_id": {
      -                "type": [
      -                  "string",
      -                  "null"
      -                ]
      -              },
      -              "to": {
      -                "items": {
      -                  "additionalProperties": false,
      -                  "properties": {
      -                    "email": {
      -                      "example": "agent@example.com",
      -                      "format": "email",
      -                      "type": "string"
      -                    },
      -                    "name": {
      -                      "example": "Support",
      -                      "type": [
      -                        "string",
      -                        "null"
      -                      ]
      -                    }
      -                  },
      -                  "required": [
      -                    "email",
      -                    "name"
      -                  ],
      -                  "type": "object"
      -                },
      -                "type": "array"
      -              }
      -            },
      -            "required": [
      -              "id",
      -              "thread_id",
      -              "folder_ids",
      -              "subject",
      -              "preview",
      -              "from",
      -              "to",
      -              "cc",
      -              "bcc",
      -              "received_at",
      -              "sent_at",
      -              "size_bytes",
      -              "has_attachments",
      -              "keywords",
      -              "flags"
      -            ],
      -            "type": "object"
      -          },
      -          {
      -            "additionalProperties": false,
      -            "properties": {
      -              "attachments": {
      -                "items": {
      -                  "additionalProperties": false,
      -                  "properties": {
      -                    "content_id": {
      -                      "description": "Content ID for inline attachments, when present.",
      -                      "type": [
      -                        "string",
      -                        "null"
      -                      ]
      -                    },
      -                    "content_type": {
      -                      "example": "application/pdf",
      -                      "type": "string"
      -                    },
      -                    "disposition": {
      -                      "example": "attachment",
      -                      "type": [
      -                        "string",
      -                        "null"
      -                      ]
      -                    },
      -                    "download_url": {
      -                      "description": "Short-lived URL for this exact attachment. Fetch it promptly; if it expires, call the message or attachment metadata endpoint again to receive a fresh URL.",
      -                      "example": "https://app.sendmux.ai/api/v1/mailbox/messages/msg_123/attachment-downloads/attref_abc123?download_token=...",
      -                      "type": "string"
      -                    },
      -                    "filename": {
      -                      "example": "invoice.pdf",
      -                      "type": [
      -                        "string",
      -                        "null"
      -                      ]
      -                    },
      -                    "id": {
      -                      "description": "Attachment blob ID.",
      -                      "type": "string"
      -                    },
      -                    "size_bytes": {
      -                      "example": 12345,
      -                      "type": [
      -                        "integer",
      -                        "null"
      -                      ]
      -                    }
      -                  },
      -                  "required": [
      -                    "id",
      -                    "filename",
      -                    "content_type",
      -                    "size_bytes",
      -                    "disposition",
      -                    "content_id"
      -                  ],
      -                  "type": "object"
      -                },
      -                "type": "array"
      -              },
      -              "html_body": {
      -                "type": [
      -                  "string",
      -                  "null"
      -                ]
      -              },
      -              "text_body": {
      -                "type": [
      -                  "string",
      -                  "null"
      -                ]
      -              }
      -            },
      -            "required": [
      -              "text_body",
      -              "html_body"
      -            ],
      -            "type": "object"
      -          }
      -        ]
      -      },
      -      "meta": {
      -        "additionalProperties": false,
      -        "properties": {
      -          "request_id": {
      -            "example": "req_clxxxxxxxxxxxxxxxxxxxxxxxxx",
      -            "type": "string"
      -          }
      -        },
      -        "required": [
      -          "request_id"
      -        ],
      -        "type": "object"
      -      }
      -    },
      -    "required": [
      -      "data"
      -    ],
      -    "type": "object"
      -  }
      -]New value: +[
      +  {
      +    "properties": {
      +      "meta": {
      +        "additionalProperties": {},
      +        "properties": {},
      +        "type": "object"
      +      },
      +      "ok": {
      +        "enum": [
      +          true
      +        ],
      +        "type": "boolean"
      +      }
      +    },
      +    "required": [
      +      "ok",
      +      "meta"
      +    ],
      +    "type": "object"
      +  },
      +  {
      +    "properties": {
      +      "data": {
      +        "additionalProperties": false,
      +        "properties": {
      +          "attachments": {
      +            "description": "Attachment metadata for this message. Each item includes a short-lived `download_url`; if it expires, fetch message metadata again.",
      +            "items": {
      +              "additionalProperties": false,
      +              "properties": {
      +                "content_id": {
      +                  "description": "Content ID for inline attachments, when present.",
      +                  "type": [
      +                    "string",
      +                    "null"
      +                  ]
      +                },
      +                "content_type": {
      +                  "example": "application/pdf",
      +                  "type": "string"
      +                },
      +                "disposition": {
      +                  "example": "attachment",
      +                  "type": [
      +                    "string",
      +                    "null"
      +                  ]
      +                },
      +                "download_url": {
      +                  "description": "Short-lived URL for this exact attachment. Fetch it promptly; if it expires, call the message or attachment metadata endpoint again to receive a fresh URL.",
      +                  "example": "https://app.sendmux.ai/api/v1/mailbox/messages/msg_123/attachment-downloads/attref_abc123?download_token=...",
      +                  "type": "string"
      +                },
      +                "filename": {
      +                  "example": "invoice.pdf",
      +                  "type": [
      +                    "string",
      +                    "null"
      +                  ]
      +                },
      +                "id": {
      +                  "description": "Attachment blob ID.",
      +                  "type": "string"
      +                },
      +                "size_bytes": {
      +                  "example": 12345,
      +                  "type": [
      +                    "integer",
      +                    "null"
      +                  ]
      +                }
      +              },
      +              "required": [
      +                "id",
      +                "filename",
      +                "content_type",
      +                "size_bytes",
      +                "disposition",
      +                "content_id"
      +              ],
      +              "type": "object"
      +            },
      +            "type": "array"
      +          },
      +          "bcc": {
      +            "items": {
      +              "additionalProperties": false,
      +              "properties": {
      +                "email": {
      +                  "example": "agent@example.com",
      +                  "format": "email",
      +                  "type": "string"
      +                },
      +                "name": {
      +                  "example": "Support",
      +                  "type": [
      +                    "string",
      +                    "null"
      +                  ]
      +                }
      +              },
      +              "required": [
      +                "email",
      +                "name"
      +              ],
      +              "type": "object"
      +            },
      +            "type": "array"
      +          },
      +          "cc": {
      +            "items": {
      +              "additionalProperties": false,
      +              "properties": {
      +                "email": {
      +                  "example": "agent@example.com",
      +                  "format": "email",
      +                  "type": "string"
      +                },
      +                "name": {
      +                  "example": "Support",
      +                  "type": [
      +                    "string",
      +                    "null"
      +                  ]
      +                }
      +              },
      +              "required": [
      +                "email",
      +                "name"
      +              ],
      +              "type": "object"
      +            },
      +            "type": "array"
      +          },
      +          "flags": {
      +            "additionalProperties": false,
      +            "properties": {
      +              "answered": {
      +                "type": "boolean"
      +              },
      +              "draft": {
      +                "type": "boolean"
      +              },
      +              "flagged": {
      +                "type": "boolean"
      +              },
      +              "seen": {
      +                "type": "boolean"
      +              }
      +            },
      +            "required": [
      +              "seen",
      +              "flagged",
      +              "draft",
      +              "answered"
      +            ],
      +            "type": "object"
      +          },
      +          "folder_ids": {
      +            "items": {
      +              "type": "string"
      +            },
      +            "type": "array"
      +          },
      +          "from": {
      +            "allOf": [
      +              {
      +                "additionalProperties": false,
      +                "properties": {
      +                  "email": {
      +                    "example": "agent@example.com",
      +                    "format": "email",
      +                    "type": "string"
      +                  },
      +                  "name": {
      +                    "example": "Support",
      +                    "type": [
      +                      "string",
      +                      "null"
      +                    ]
      +                  }
      +                },
      +                "required": [
      +                  "email",
      +                  "name"
      +                ],
      +                "type": "object"
      +              },
      +              {
      +                "type": [
      +                  "object",
      +                  "null"
      +                ]
      +              }
      +            ]
      +          },
      +          "has_attachments": {
      +            "type": "boolean"
      +          },
      +          "html_body": {
      +            "type": [
      +              "string",
      +              "null"
      +            ]
      +          },
      +          "id": {
      +            "description": "Message ID",
      +            "type": "string"
      +          },
      +          "keywords": {
      +            "description": "Active message keywords, including system flags and custom labels.",
      +            "example": [
      +              "$seen",
      +              "$flagged",
      +              "agent_triaged"
      +            ],
      +            "items": {
      +              "type": "string"
      +            },
      +            "type": "array"
      +          },
      +          "preview": {
      +            "type": [
      +              "string",
      +              "null"
      +            ]
      +          },
      +          "received_at": {
      +            "type": [
      +              "string",
      +              "null"
      +            ]
      +          },
      +          "sent_at": {
      +            "type": [
      +              "string",
      +              "null"
      +            ]
      +          },
      +          "size_bytes": {
      +            "type": [
      +              "integer",
      +              "null"
      +            ]
      +          },
      +          "subject": {
      +            "type": [
      +              "string",
      +              "null"
      +            ]
      +          },
      +          "text_body": {
      +            "type": [
      +              "string",
      +              "null"
      +            ]
      +          },
      +          "thread_id": {
      +            "type": [
      +              "string",
      +              "null"
      +            ]
      +          },
      +          "to": {
      +            "items": {
      +              "additionalProperties": false,
      +              "properties": {
      +                "email": {
      +                  "example": "agent@example.com",
      +                  "format": "email",
      +                  "type": "string"
      +                },
      +                "name": {
      +                  "example": "Support",
      +                  "type": [
      +                    "string",
      +                    "null"
      +                  ]
      +                }
      +              },
      +              "required": [
      +                "email",
      +                "name"
      +              ],
      +              "type": "object"
      +            },
      +            "type": "array"
      +          }
      +        },
      +        "required": [
      +          "id",
      +          "thread_id",
      +          "folder_ids",
      +          "subject",
      +          "preview",
      +          "from",
      +          "to",
      +          "cc",
      +          "bcc",
      +          "received_at",
      +          "sent_at",
      +          "size_bytes",
      +          "has_attachments",
      +          "keywords",
      +          "flags",
      +          "text_body",
      +          "html_body"
      +        ],
      +        "type": "object"
      +      },
      +      "meta": {
      +        "additionalProperties": false,
      +        "properties": {
      +          "request_id": {
      +            "example": "req_clxxxxxxxxxxxxxxxxxxxxxxxxx",
      +            "type": "string"
      +          }
      +        },
      +        "required": [
      +          "request_id"
      +        ],
      +        "type": "object"
      +      }
      +    },
      +    "required": [
      +      "data"
      +    ],
      +    "type": "object"
      +  }
      +]
  3. Changed4 schema fields changedv1.0.8
    • addedOutput schema / $schema
      Added value: +"https://json-schema.org/draft/2020-12/schema"
    • removedOutput schema / additionalProperties
      Removed value: -true
    • addedOutput schema / properties
      Added value: +{
      +  "result": {
      +    "allOf": [
      +      {
      +        "properties": {
      +          "meta": {
      +            "additionalProperties": {},
      +            "properties": {},
      +            "type": "object"
      +          },
      +          "ok": {
      +            "enum": [
      +              true
      +            ],
      +            "type": "boolean"
      +          }
      +        },
      +        "required": [
      +          "ok",
      +          "meta"
      +        ],
      +        "type": "object"
      +      },
      +      {
      +        "properties": {
      +          "data": {
      +            "allOf": [
      +              {
      +                "additionalProperties": false,
      +                "properties": {
      +                  "attachments": {
      +                    "description": "Attachment metadata for this message. Each item includes a short-lived `download_url`; if it expires, fetch message metadata again.",
      +                    "items": {
      +                      "additionalProperties": false,
      +                      "properties": {
      +                        "content_id": {
      +                          "description": "Content ID for inline attachments, when present.",
      +                          "type": [
      +                            "string",
      +                            "null"
      +                          ]
      +                        },
      +                        "content_type": {
      +                          "example": "application/pdf",
      +                          "type": "string"
      +                        },
      +                        "disposition": {
      +                          "example": "attachment",
      +                          "type": [
      +                            "string",
      +                            "null"
      +                          ]
      +                        },
      +                        "download_url": {
      +                          "description": "Short-lived URL for this exact attachment. Fetch it promptly; if it expires, call the message or attachment metadata endpoint again to receive a fresh URL.",
      +                          "example": "https://app.sendmux.ai/api/v1/mailbox/messages/msg_123/attachment-downloads/attref_abc123?download_token=...",
      +                          "type": "string"
      +                        },
      +                        "filename": {
      +                          "example": "invoice.pdf",
      +                          "type": [
      +                            "string",
      +                            "null"
      +                          ]
      +                        },
      +                        "id": {
      +                          "description": "Attachment blob ID.",
      +                          "type": "string"
      +                        },
      +                        "size_bytes": {
      +                          "example": 12345,
      +                          "type": [
      +                            "integer",
      +                            "null"
      +                          ]
      +                        }
      +                      },
      +                      "required": [
      +                        "id",
      +                        "filename",
      +                        "content_type",
      +                        "size_bytes",
      +                        "disposition",
      +                        "content_id"
      +                      ],
      +                      "type": "object"
      +                    },
      +                    "type": "array"
      +                  },
      +                  "bcc": {
      +                    "items": {
      +                      "additionalProperties": false,
      +                      "properties": {
      +                        "email": {
      +                          "example": "agent@example.com",
      +                          "format": "email",
      +                          "type": "string"
      +                        },
      +                        "name": {
      +                          "example": "Support",
      +                          "type": [
      +                            "string",
      +                            "null"
      +                          ]
      +                        }
      +                      },
      +                      "required": [
      +                        "email",
      +                        "name"
      +                      ],
      +                      "type": "object"
      +                    },
      +                    "type": "array"
      +                  },
      +                  "cc": {
      +                    "items": {
      +                      "additionalProperties": false,
      +                      "properties": {
      +                        "email": {
      +                          "example": "agent@example.com",
      +                          "format": "email",
      +                          "type": "string"
      +                        },
      +                        "name": {
      +                          "example": "Support",
      +                          "type": [
      +                            "string",
      +                            "null"
      +                          ]
      +                        }
      +                      },
      +                      "required": [
      +                        "email",
      +                        "name"
      +                      ],
      +                      "type": "object"
      +                    },
      +                    "type": "array"
      +                  },
      +                  "flags": {
      +                    "additionalProperties": false,
      +                    "properties": {
      +                      "answered": {
      +                        "type": "boolean"
      +                      },
      +                      "draft": {
      +                        "type": "boolean"
      +                      },
      +                      "flagged": {
      +                        "type": "boolean"
      +                      },
      +                      "seen": {
      +                        "type": "boolean"
      +                      }
      +                    },
      +                    "required": [
      +                      "seen",
      +                      "flagged",
      +                      "draft",
      +                      "answered"
      +                    ],
      +                    "type": "object"
      +                  },
      +                  "folder_ids": {
      +                    "items": {
      +                      "type": "string"
      +                    },
      +                    "type": "array"
      +                  },
      +                  "from": {
      +                    "allOf": [
      +                      {
      +                        "additionalProperties": false,
      +                        "properties": {
      +                          "email": {
      +                            "example": "agent@example.com",
      +                            "format": "email",
      +                            "type": "string"
      +                          },
      +                          "name": {
      +                            "example": "Support",
      +                            "type": [
      +                              "string",
      +                              "null"
      +                            ]
      +                          }
      +                        },
      +                        "required": [
      +                          "email",
      +                          "name"
      +                        ],
      +                        "type": "object"
      +                      },
      +                      {
      +                        "type": [
      +                          "object",
      +                          "null"
      +                        ]
      +                      }
      +                    ]
      +                  },
      +                  "has_attachments": {
      +                    "type": "boolean"
      +                  },
      +                  "id": {
      +                    "description": "Message ID",
      +                    "type": "string"
      +                  },
      +                  "keywords": {
      +                    "description": "Active message keywords, including system flags and custom labels.",
      +                    "example": [
      +                      "$seen",
      +                      "$flagged",
      +                      "agent_triaged"
      +                    ],
      +                    "items": {
      +                      "type": "string"
      +                    },
      +                    "type": "array"
      +                  },
      +                  "preview": {
      +                    "type": [
      +                      "string",
      +                      "null"
      +                    ]
      +                  },
      +                  "received_at": {
      +                    "type": [
      +                      "string",
      +                      "null"
      +                    ]
      +                  },
      +                  "sent_at": {
      +                    "type": [
      +                      "string",
      +                      "null"
      +                    ]
      +                  },
      +                  "size_bytes": {
      +                    "type": [
      +                      "integer",
      +                      "null"
      +                    ]
      +                  },
      +                  "subject": {
      +                    "type": [
      +                      "string",
      +                      "null"
      +                    ]
      +                  },
      +                  "thread_id": {
      +                    "type": [
      +                      "string",
      +                      "null"
      +                    ]
      +                  },
      +                  "to": {
      +                    "items": {
      +                      "additionalProperties": false,
      +                      "properties": {
      +                        "email": {
      +                          "example": "agent@example.com",
      +                          "format": "email",
      +                          "type": "string"
      +                        },
      +                        "name": {
      +                          "example": "Support",
      +                          "type": [
      +                            "string",
      +                            "null"
      +                          ]
      +                        }
      +                      },
      +                      "required": [
      +                        "email",
      +                        "name"
      +                      ],
      +                      "type": "object"
      +                    },
      +                    "type": "array"
      +                  }
      +                },
      +                "required": [
      +                  "id",
      +                  "thread_id",
      +                  "folder_ids",
      +                  "subject",
      +                  "preview",
      +                  "from",
      +                  "to",
      +                  "cc",
      +                  "bcc",
      +                  "received_at",
      +                  "sent_at",
      +                  "size_bytes",
      +                  "has_attachments",
      +                  "keywords",
      +                  "flags"
      +                ],
      +                "type": "object"
      +              },
      +              {
      +                "additionalProperties": false,
      +                "properties": {
      +                  "attachments": {
      +                    "items": {
      +                      "additionalProperties": false,
      +                      "properties": {
      +                        "content_id": {
      +                          "description": "Content ID for inline attachments, when present.",
      +                          "type": [
      +                            "string",
      +                            "null"
      +                          ]
      +                        },
      +                        "content_type": {
      +                          "example": "application/pdf",
      +                          "type": "string"
      +                        },
      +                        "disposition": {
      +                          "example": "attachment",
      +                          "type": [
      +                            "string",
      +                            "null"
      +                          ]
      +                        },
      +                        "download_url": {
      +                          "description": "Short-lived URL for this exact attachment. Fetch it promptly; if it expires, call the message or attachment metadata endpoint again to receive a fresh URL.",
      +                          "example": "https://app.sendmux.ai/api/v1/mailbox/messages/msg_123/attachment-downloads/attref_abc123?download_token=...",
      +                          "type": "string"
      +                        },
      +                        "filename": {
      +                          "example": "invoice.pdf",
      +                          "type": [
      +                            "string",
      +                            "null"
      +                          ]
      +                        },
      +                        "id": {
      +                          "description": "Attachment blob ID.",
      +                          "type": "string"
      +                        },
      +                        "size_bytes": {
      +                          "example": 12345,
      +                          "type": [
      +                            "integer",
      +                            "null"
      +                          ]
      +                        }
      +                      },
      +                      "required": [
      +                        "id",
      +                        "filename",
      +                        "content_type",
      +                        "size_bytes",
      +                        "disposition",
      +                        "content_id"
      +                      ],
      +                      "type": "object"
      +                    },
      +                    "type": "array"
      +                  },
      +                  "html_body": {
      +                    "type": [
      +                      "string",
      +                      "null"
      +                    ]
      +                  },
      +                  "text_body": {
      +                    "type": [
      +                      "string",
      +                      "null"
      +                    ]
      +                  }
      +                },
      +                "required": [
      +                  "text_body",
      +                  "html_body"
      +                ],
      +                "type": "object"
      +              }
      +            ]
      +          },
      +          "meta": {
      +            "additionalProperties": false,
      +            "properties": {
      +              "request_id": {
      +                "example": "req_clxxxxxxxxxxxxxxxxxxxxxxxxx",
      +                "type": "string"
      +              }
      +            },
      +            "required": [
      +              "request_id"
      +            ],
      +            "type": "object"
      +          }
      +        },
      +        "required": [
      +          "data"
      +        ],
      +        "type": "object"
      +      }
      +    ],
      +    "unevaluatedProperties": {
      +      "not": {}
      +    },
      +    "x-fastmcp-top-level-schema": "MailboxMessageDetailResponse"
      +  }
      +}
    • addedOutput schema / required
      Added value: +[
      +  "result"
      +]
  4. First observedv1.0.0

TDQS

A4.4/5.0
Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint, idempotentHint, and non-destructive behavior, so the safety profile is covered. The description adds that it fetches a summary or detail, implying a non-body response, and the reference to body tools reinforces that. It does not detail error behavior or return format, but the output schema covers that. No contradiction with annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences with zero waste: the first states the core purpose and scope, the second provides the routing rule. The most important information is front-loaded, and every word earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the output schema and comprehensive annotations, the description provides sufficient context for correct invocation. It explains when to use this tool versus body-content alternatives, and the schema handles parameter details. A slightly more explicit statement about the absence of body content in the response would improve it, but it is already implied.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, and the schema already documents all three parameters with clear descriptions. The tool description does not add any meaning beyond restating that it uses message_id. Baseline of 3 is appropriate when schema fully handles parameter semantics.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

Description clearly states the verb (fetch) and resource (one message) keyed by message_id, and explicitly differentiates from sibling tools by noting that body content is not returned here. It distinguishes from mailbox_batch_get_messages by saying 'one message' and from body-fetching tools by naming them.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Provides explicit when-not guidance: 'Use mailbox_list_body or mailbox_list_content when the body content is required.' This gives the agent a clear decision rule and names the alternatives, leaving no ambiguity about when to select this tool.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.