MCP Emails

List Inboxes

inbox_list

Read-onlyIdempotent

Retrieve all available email inboxes for an API key, including IDs, addresses, providers, and capabilities. Use this first to obtain the inbox_id required by other email tools.

Instructions

List every inbox (mailbox or account) this API key may use. Call it FIRST for the inbox_id the other tools take. Each entry carries the UUID, email address, display name, provider, optional service brand (icloud/yahoo/zoho/yandex/generic) and a capabilities object.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`provider`	No	Return only inboxes served by this provider. Omit for all of them.
`include_capabilities`	No	Include each inbox's capabilities object. Set false for a compact list of inbox_id, email address, display name, provider and brand.

Output Schema

TableJSON Schema

Name	Required	Description	Default
`notes`	No	Server notes about how this call was handled — for example an argument that was not applied because the selected action does not accept it. Written by MCP Emails, not taken from any message, and absent when there is nothing to report.
`inboxes`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 10, 2026

addedOutput schema / properties / notes

Added value: +{
+  "description": "Server notes about how this call was handled — for example an argument that was not applied because the selected action does not accept it. Written by MCP Emails, not taken from any message, and absent when there is nothing to report.",
+  "items": {
+    "type": "string"
+  },
+  "type": "array"
+}

First observedv1.0.4Aug 30, 2026

TDQS

A4.5/5.0

Behavior4/5

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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds behavioral context by stating the tool returns all inboxes the API key may use, and enumerates the fields in each entry, including optional brand and capabilities. It doesn't mention pagination or rate limits, but for a read-only list tool this is adequate.

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?

Three sentences, all informative. The first sentence front-loads the core purpose and the critical usage instruction. The second sentence explains the return fields. No wasted words.

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

Completeness5/5

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

The tool has an output schema, so return values are already documented. The description covers the essential context: what the tool lists, why it matters (inbox_id for other tools), and what each entry contains. For a simple read-only list tool with full schema coverage, this is 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 description coverage is 100%, so the schema already documents both parameters fully. The description adds context about the capabilities object and brand field, but doesn't add meaning beyond the schema for the parameters themselves. 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?

The description states a specific verb ('List') and resource ('every inbox'), and clarifies that it returns the inbox_id used by other tools. It distinguishes itself from siblings like folder_list and draft_list by naming the resource type and the fields returned.

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?

Explicitly instructs the agent to call it FIRST to obtain the inbox_id required by other tools. This is clear when-to-use guidance that no sibling provides, and it also implies when not to use it (when you already have an inbox_id).

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