Sendmux Email Inbox API + Sending

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Read Message Body

mailbox_list_body

Read-onlyIdempotent

Retrieve the plain text or HTML body of an email by message ID, skipping MIME details. Specify the desired part and optional character limit to get exactly the message content needed.

Instructions

Use this to read the raw or simplified body for a known message_id. Prefer it when the task needs message text but not every MIME detail.

Input Schema

TableJSON Schema

Name	Required	Description
`part`	No	Body part to return.
`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.
`message_id`	Yes	Message ID.
`If-None-Match`	No	Weak ETag from a previous response. Returns 304 when unchanged.
`max_body_chars`	No	Maximum body characters to return before truncation.

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": {
-        "allOf": [
-          {
-            "additionalProperties": false,
-            "properties": {
-              "body": {
-                "additionalProperties": false,
-                "properties": {
-                  "html": {
-                    "type": [
-                      "string",
-                      "null"
-                    ]
-                  },
-                  "is_truncated": {
-                    "type": "boolean"
-                  },
-                  "text": {
-                    "type": [
-                      "string",
-                      "null"
-                    ]
-                  },
-                  "truncated_at_chars": {
-                    "type": [
-                      "integer",
-                      "null"
-                    ]
-                  }
-                },
-                "required": [
-                  "text",
-                  "html",
-                  "is_truncated",
-                  "truncated_at_chars"
-                ],
-                "type": "object"
-              },
-              "id": {
-                "description": "Message ID",
-                "type": "string"
-              },
-              "part": {
-                "enum": [
-                  "text",
-                  "html",
-                  "both"
-                ],
-                "type": "string"
-              },
-              "states": {
-                "additionalProperties": false,
-                "properties": {
-                  "email_state": {
-                    "type": [
-                      "string",
-                      "null"
-                    ]
-                  }
-                },
-                "required": [
-                  "email_state"
-                ],
-                "type": "object"
-              },
-              "thread_id": {
-                "type": [
-                  "string",
-                  "null"
-                ]
-              }
-            },
-            "required": [
-              "id",
-              "thread_id",
-              "part",
-              "body",
-              "states"
-            ],
-            "type": [
-              "object",
-              "null"
-            ]
-          },
-          {
-            "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": {
+          "body": {
+            "additionalProperties": false,
+            "properties": {
+              "html": {
+                "type": [
+                  "string",
+                  "null"
+                ]
+              },
+              "is_truncated": {
+                "type": "boolean"
+              },
+              "text": {
+                "type": [
+                  "string",
+                  "null"
+                ]
+              },
+              "truncated_at_chars": {
+                "type": [
+                  "integer",
+                  "null"
+                ]
+              }
+            },
+            "required": [
+              "text",
+              "html",
+              "is_truncated",
+              "truncated_at_chars"
+            ],
+            "type": "object"
+          },
+          "id": {
+            "description": "Message ID",
+            "type": "string"
+          },
+          "part": {
+            "enum": [
+              "text",
+              "html",
+              "both"
+            ],
+            "type": "string"
+          },
+          "states": {
+            "additionalProperties": false,
+            "properties": {
+              "email_state": {
+                "type": [
+                  "string",
+                  "null"
+                ]
+              }
+            },
+            "required": [
+              "email_state"
+            ],
+            "type": "object"
+          },
+          "thread_id": {
+            "type": [
+              "string",
+              "null"
+            ]
+          }
+        },
+        "required": [
+          "id",
+          "thread_id",
+          "part",
+          "body",
+          "states"
+        ],
+        "type": "object"
+      },
+      "meta": {
+        "additionalProperties": false,
+        "properties": {
+          "request_id": {
+            "example": "req_clxxxxxxxxxxxxxxxxxxxxxxxxx",
+            "type": "string"
+          }
+        },
+        "required": [
+          "request_id"
+        ],
+        "type": "object"
+      }
+    },
+    "required": [
+      "data"
+    ],
+    "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": {
+            "allOf": [
+              {
+                "additionalProperties": false,
+                "properties": {
+                  "body": {
+                    "additionalProperties": false,
+                    "properties": {
+                      "html": {
+                        "type": [
+                          "string",
+                          "null"
+                        ]
+                      },
+                      "is_truncated": {
+                        "type": "boolean"
+                      },
+                      "text": {
+                        "type": [
+                          "string",
+                          "null"
+                        ]
+                      },
+                      "truncated_at_chars": {
+                        "type": [
+                          "integer",
+                          "null"
+                        ]
+                      }
+                    },
+                    "required": [
+                      "text",
+                      "html",
+                      "is_truncated",
+                      "truncated_at_chars"
+                    ],
+                    "type": "object"
+                  },
+                  "id": {
+                    "description": "Message ID",
+                    "type": "string"
+                  },
+                  "part": {
+                    "enum": [
+                      "text",
+                      "html",
+                      "both"
+                    ],
+                    "type": "string"
+                  },
+                  "states": {
+                    "additionalProperties": false,
+                    "properties": {
+                      "email_state": {
+                        "type": [
+                          "string",
+                          "null"
+                        ]
+                      }
+                    },
+                    "required": [
+                      "email_state"
+                    ],
+                    "type": "object"
+                  },
+                  "thread_id": {
+                    "type": [
+                      "string",
+                      "null"
+                    ]
+                  }
+                },
+                "required": [
+                  "id",
+                  "thread_id",
+                  "part",
+                  "body",
+                  "states"
+                ],
+                "type": [
+                  "object",
+                  "null"
+                ]
+              },
+              {
+                "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": "MailboxRawBodyResponse"
+  }
+}

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 establish read-only, idempotent, open-world, and non-destructive behavior. The description adds useful behavioral context about response granularity (raw/simplified body, not full MIME details), which goes beyond what annotations express.

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 no filler. The verb, resource, precondition, and selection guidance are front-loaded and every sentence 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?

The schema covers all parameters, an output schema exists, and annotations cover safety guarantees. The description provides enough decision context for an agent to invoke the tool correctly, though explicit sibling routing for full-MIME or attachment needs would make it fully complete.

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%, so the baseline is 3. The description adds general context about body versus MIME details but does not explain parameter-specific behavior beyond what the schema already provides.

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?

The description states a specific verb ('read'), a specific resource ('body'), and a precise scope ('for a known message_id'). It also distinguishes the tool from generic message retrieval by clarifying that it returns raw or simplified body content and omits full MIME detail.

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?

The description gives an explicit preference condition: use it when the task needs message text but not every MIME detail. This gives an agent useful selection context, though it does not name specific alternative tools or explicitly say when not to use it.

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