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List Mailbox Identities

mailbox_list_identities

Read-onlyIdempotent

List sender identities available for a mailbox to identify valid from-addresses for sending emails, with pagination for large sets.

Instructions

Use this to list sender identities available to the mailbox. Prefer mailbox_get_identity when only the default identity is needed.

Input Schema

TableJSON Schema

Name	Required	Description
`limit`	No	Maximum results (default 50, max 100).
`cursor`	No	Pagination cursor — the `next_cursor` from the previous response.
`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.

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": {
+            "items": {
+              "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"
+            },
+            "type": "array"
+          },
+          "meta": {
+            "additionalProperties": false,
+            "properties": {
+              "identity_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": "MailboxIdentityCursorListResponse"
+  }
+}

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?

The annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is fully covered. The description does not add additional behavioral context (e.g., pagination details or rate limits), but with the output schema present and the annotations strong, a baseline 3 is appropriate.

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 fluff. The primary purpose is in the first sentence, and the sibling distinction is delivered concisely in the second. 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 that the output schema is present (so return format is documented), the annotations cover safety, and the parameters are fully explained in the schema, the description covers all essential decision points. It could add a note on pagination behavior, but the cursor parameter implies it, making this a minor gap. Overall, it's complete for an agent to call correctly.

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%, meaning all three parameters (limit, cursor, mailbox_id) already have clear documentation in the schema. The tool description does not add any extra nuance beyond what the schema provides, so it meets the baseline of 3 without adding value.

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 clear verb ('list') and specific resource ('sender identities available to the mailbox'), and it explicitly differentiates from the sibling mailbox_get_identity by naming the condition under which that alternative is preferred. This leaves no ambiguity about what the tool does.

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 explicitly tells when to use this tool (to list all identities) and when to prefer the alternative 'mailbox_get_identity' when only the default identity is needed. This provides direct routing guidance without requiring inference.

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