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Update Mailbox Identity

mailbox_update_identity

Idempotent

Update a mailbox's sender identity by changing the sender name, HTML signature, or plain text signature, ensuring future sends use the correct identity.

Instructions

Use this only when the user explicitly asks to change sender identity details. Do not use it for one-off message composition.

Input Schema

TableJSON Schema

Name	Required	Description
`name`	No	Default sender name. Send null or an empty string to clear it.
`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.
`html_signature`	No	HTML signature appended to Mailbox API sends that include html_body.
`text_signature`	No	Plain text signature appended to Mailbox API sends that include text_body.

Output Schema

TableJSON Schema

Name	Required	Description	Default
`result`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

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": {
+            "additionalProperties": false,
+            "properties": {
+              "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"
+              },
+              "email": {
+                "format": "email",
+                "type": "string"
+              },
+              "html_signature": {
+                "type": "string"
+              },
+              "id": {
+                "description": "Identity ID",
+                "type": "string"
+              },
+              "may_delete": {
+                "description": "Whether the mailbox service allows this identity to be deleted.",
+                "type": "boolean"
+              },
+              "name": {
+                "type": "string"
+              },
+              "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"
+              },
+              "text_signature": {
+                "type": "string"
+              }
+            },
+            "required": [
+              "id",
+              "name",
+              "email",
+              "reply_to",
+              "bcc",
+              "text_signature",
+              "html_signature",
+              "may_delete"
+            ],
+            "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": "MailboxIdentityResponse"
+  }
+}

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

First observedv1.0.0Jul 13, 2026

TDQS

A4.2/5.0

Behavior3/5

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

Annotations already declare readOnlyHint=false, idempotentHint=true, and destructiveHint=false, so the safe mutation profile is known. The description adds a usage boundary (not for one-off composition) but does not disclose additional behavioral details such as persistence, overwrite semantics, or whether omitted fields are preserved. There is 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?

The description is two sentences with no filler. The critical usage condition is front-loaded, and the exclusion is stated immediately afterward. 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?

For an update tool with zero required parameterslint, the schema covers all fields, the output schema exists, and annotations cover idempotency/destructiveness. The description covers when to use it and what not to use it for. The only noticeable gap is explicit partial-update semantics — whether omitted fields are preserved — which is a minor omission given the schema and annotations.

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%, and each parameter already has meaningful descriptions, including null-clearing semantics for name and signature fields and mailbox_id scoping guidance. The description does not add parameter-level meaning beyond labeling the operation as changing sender identity details, so the baseline of 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?

The description states the action with a specific verb and resource: 'change sender identity details.' It also explicitly distinguishes this from 'one-off message composition,' separating it from sending-related siblings. The title reinforces the target resource, so an agent can identify what this tool changes.

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?

The description gives an explicit trigger condition: 'only when the user explicitly asks to change sender identity details.' It also provides a clear exclusion: 'Do not use it for one-off message composition,' which prevents confusing this with sending tools. This is direct, actionable usage guidance.

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