Sendmux Email Inbox API + Sending

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Overview Schema Source Related Servers Discussions Admin

List Threads

mailbox_list_threads

Read-onlyIdempotent

Scan email conversation threads without loading every message. Filter by search, folder, unread status, attachments, participant, or date to pinpoint relevant threads.

Instructions

Use this to scan conversation threads without loading every message. Continue with next_cursor only when additional threads are needed.

Input Schema

TableJSON Schema

Name	Required	Description
`q`	No	Full-text search query across thread messages.
`after`	No	Filter to threads updated after this ISO 8601 timestamp.
`limit`	No	Maximum results (default 50, max 100).
`before`	No	Filter to threads updated before this ISO 8601 timestamp.
`cursor`	No	Pagination cursor — the `next_cursor` from the previous response.
`folder_id`	No	Filter to threads with messages in this folder ID.
`is_unread`	No	When true, only return threads with unread messages.
`mailbox_id`	No	Mailbox public ID to target when the credential grants access to more than one mailbox. Omit when the credential is scoped to exactly one mailbox.
`participant`	No	Filter by participant email address or display name.
`has_attachment`	No	When true, only return threads with attachments.
`sort_direction`	No	Sort direction.

Output Schema

TableJSON Schema

Name	Required	Description	Default
`result`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedv1.0.14Sep 23, 2026

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": {
-        "items": {
-          "additionalProperties": false,
-          "properties": {
-            "folder_ids": {
-              "items": {
-                "type": "string"
-              },
-              "type": "array"
-            },
-            "has_attachments": {
-              "type": "boolean"
-            },
-            "id": {
-              "description": "Thread ID",
-              "type": "string"
-            },
-            "last_message": {
-              "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"
-                },
-                {
-                  "type": [
-                    "object",
-                    "null"
-                  ]
-                }
-              ]
-            },
-            "message_count": {
-              "type": "integer"
-            },
-            "participants": {
-              "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"
-            },
-            "states": {
-              "additionalProperties": false,
-              "properties": {
-                "email_state": {
-                  "type": [
-                    "string",
-                    "null"
-                  ]
-                },
-                "thread_state": {
-                  "type": [
-                    "string",
-                    "null"
-                  ]
-                }
-              },
-              "required": [
-                "thread_state",
-                "email_state"
-              ],
-              "type": "object"
-            },
-            "subject": {
-              "type": [
-                "string",
-                "null"
-              ]
-            },
-            "unread_count": {
-              "type": "integer"
-            }
-          },
-          "required": [
-            "id",
-            "subject",
-            "message_count",
-            "unread_count",
-            "has_attachments",
-            "folder_ids",
-            "participants",
-            "last_message",
-            "states"
-          ],
-          "type": "object"
-        },
-        "type": "array"
-      },
-      "meta": {
-        "additionalProperties": false,
-        "properties": {
-          "query_state": {
-            "type": "string"
-          },
-          "request_id": {
-            "type": "string"
-          }
-        },
-        "required": [
-          "request_id"
-        ],
-        "type": "object"
-      },
-      "pagination": {
-        "additionalProperties": false,
-        "properties": {
-          "has_more": {
-            "type": "boolean"
-          },
-          "next_cursor": {
-            "type": "string"
-          }
-        },
-        "required": [
-          "has_more"
-        ],
-        "type": "object"
-      }
-    },
-    "required": [
-      "data",
-      "pagination"
-    ],
-    "type": "object"
-  }
-]New value: +[
+  {
+    "properties": {
+      "meta": {
+        "additionalProperties": {},
+        "properties": {},
+        "type": "object"
+      },
+      "ok": {
+        "enum": [
+          true
+        ],
+        "type": "boolean"
+      }
+    },
+    "required": [
+      "ok",
+      "meta"
+    ],
+    "type": "object"
+  },
+  {
+    "properties": {
+      "data": {
+        "items": {
+          "additionalProperties": false,
+          "properties": {
+            "folder_ids": {
+              "items": {
+                "type": "string"
+              },
+              "type": "array"
+            },
+            "has_attachments": {
+              "type": "boolean"
+            },
+            "id": {
+              "description": "Thread ID",
+              "type": "string"
+            },
+            "last_message": {
+              "anyOf": [
+                {
+                  "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"
+                    },
+                    "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"
+                },
+                {
+                  "type": "null"
+                }
+              ]
+            },
+            "message_count": {
+              "type": "integer"
+            },
+            "participants": {
+              "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"
+            },
+            "states": {
+              "additionalProperties": false,
+              "properties": {
+                "email_state": {
+                  "type": [
+                    "string",
+                    "null"
+                  ]
+                },
+                "thread_state": {
+                  "type": [
+                    "string",
+                    "null"
+                  ]
+                }
+              },
+              "required": [
+                "thread_state",
+                "email_state"
+              ],
+              "type": "object"
+            },
+            "subject": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
+            "unread_count": {
+              "type": "integer"
+            }
+          },
+          "required": [
+            "id",
+            "subject",
+            "message_count",
+            "unread_count",
+            "has_attachments",
+            "folder_ids",
+            "participants",
+            "last_message",
+            "states"
+          ],
+          "type": "object"
+        },
+        "type": "array"
+      },
+      "meta": {
+        "additionalProperties": false,
+        "properties": {
+          "query_state": {
+            "type": "string"
+          },
+          "request_id": {
+            "type": "string"
+          }
+        },
+        "required": [
+          "request_id"
+        ],
+        "type": "object"
+      },
+      "pagination": {
+        "additionalProperties": false,
+        "properties": {
+          "has_more": {
+            "type": "boolean"
+          },
+          "next_cursor": {
+            "type": "string"
+          }
+        },
+        "required": [
+          "has_more"
+        ],
+        "type": "object"
+      }
+    },
+    "required": [
+      "data",
+      "pagination"
+    ],
+    "type": "object"
+  }
+]

Changed4 schema fields changedv1.0.8Sep 15, 2026

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": {
+            "items": {
+              "additionalProperties": false,
+              "properties": {
+                "folder_ids": {
+                  "items": {
+                    "type": "string"
+                  },
+                  "type": "array"
+                },
+                "has_attachments": {
+                  "type": "boolean"
+                },
+                "id": {
+                  "description": "Thread ID",
+                  "type": "string"
+                },
+                "last_message": {
+                  "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"
+                    },
+                    {
+                      "type": [
+                        "object",
+                        "null"
+                      ]
+                    }
+                  ]
+                },
+                "message_count": {
+                  "type": "integer"
+                },
+                "participants": {
+                  "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"
+                },
+                "states": {
+                  "additionalProperties": false,
+                  "properties": {
+                    "email_state": {
+                      "type": [
+                        "string",
+                        "null"
+                      ]
+                    },
+                    "thread_state": {
+                      "type": [
+                        "string",
+                        "null"
+                      ]
+                    }
+                  },
+                  "required": [
+                    "thread_state",
+                    "email_state"
+                  ],
+                  "type": "object"
+                },
+                "subject": {
+                  "type": [
+                    "string",
+                    "null"
+                  ]
+                },
+                "unread_count": {
+                  "type": "integer"
+                }
+              },
+              "required": [
+                "id",
+                "subject",
+                "message_count",
+                "unread_count",
+                "has_attachments",
+                "folder_ids",
+                "participants",
+                "last_message",
+                "states"
+              ],
+              "type": "object"
+            },
+            "type": "array"
+          },
+          "meta": {
+            "additionalProperties": false,
+            "properties": {
+              "query_state": {
+                "type": "string"
+              },
+              "request_id": {
+                "type": "string"
+              }
+            },
+            "required": [
+              "request_id"
+            ],
+            "type": "object"
+          },
+          "pagination": {
+            "additionalProperties": false,
+            "properties": {
+              "has_more": {
+                "type": "boolean"
+              },
+              "next_cursor": {
+                "type": "string"
+              }
+            },
+            "required": [
+              "has_more"
+            ],
+            "type": "object"
+          }
+        },
+        "required": [
+          "data",
+          "pagination"
+        ],
+        "type": "object"
+      }
+    ],
+    "unevaluatedProperties": {
+      "not": {}
+    },
+    "x-fastmcp-top-level-schema": "MailboxThreadSummaryCursorListResponse"
+  }
+}

addedOutput schema / required
```
Added value: +[
+  "result"
+]
```

First observedv1.0.0Jul 13, 2026

TDQS

A4.2/5.0

Behavior4/5

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

Annotations already cover read-only, idempotent, non-destructive, so the description's job is to add nuance. It adds that this is a lightweight scan that avoids loading every message and that next_cursor should only be followed when more threads are needed. 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, no filler, and the core purpose is front-loaded before the pagination note. Every sentence carries weight.

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?

With full schema coverage and an output schema, the description covers the essential purpose and pagination behavior. It could be stronger by naming the sibling tools for thread detail/message listing, but nothing needed to invoke correctly is missing.

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 description coverage is 100%, so the schema documents all 11 parameters. The description adds no new parameter-level detail beyond reinforcing cursor pagination, so the baseline 3 is appropriate.

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?

States a clear verb-resource pair: scan conversation threads. 'Without loading every message' differentiates it from message-body tools like mailbox_get_message and mailbox_list_thread_messages.

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

Usage Guidelines4/5

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

Gives a clear usage context (thread-level scanning) and pagination guidance ('Continue with next_cursor only when additional threads are needed'). It does not explicitly name sibling alternatives or state when not to use it, so it stops short of a 5.

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