Fastmail MCP Server

delete_mailbox

Delete a mailbox folder, either empty or with force to move its emails to Trash. System mailboxes cannot be deleted.

Instructions

Delete a mailbox (folder). The mailbox must be empty or you must set force=true to delete with all contents. System mailboxes (Inbox, Trash, etc.) cannot be deleted.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "mailboxId": "<mailboxId>"
    },
    "name": "delete_mailbox"
  }
}

Input Schema

Name	Required	Description	Default
`force`	No	Set to true to delete the mailbox even if it contains emails (moves emails to Trash). Default: false (only delete if empty).
`mailboxId`	Yes	The mailbox ID to delete

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.3.0Aug 2, 2026

TDQS

A4.2/5.0

Behavior4/5

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

With no annotations, the description carries the full burden. It discloses the empty-required constraint, the force=true override, and the restriction on system mailboxes. It could also mention the permanent nature of deletion or that force moves emails to Trash, but the latter is covered by the force parameter description. The phrase 'delete with all contents' is slightly ambiguous but acceptable.

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, front-loaded with the action, and every sentence provides necessary constraints (empty requirement, force behavior, system mailbox exclusion). No wasted words.

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 a mailbox deletion tool, the description includes key operational constraints and exceptions. The schema handles parameter details, and there is no output schema to explain. It could mention return values or required permissions, but the description is largely complete for the tool's simplicity.

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?

The input schema already provides descriptions for both parameters (mailboxId and force), and the description only reiterates force=true without adding new parameter semantics. This meets the baseline of 3 for high schema coverage.

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 clearly states 'Delete a mailbox (folder)' with a specific verb and resource, distinguishing it from sibling tools like delete_email and delete_calendar_event. Clarifying that a mailbox is a folder adds useful context.

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 provides clear usage conditions: the mailbox must be empty or force=true is required, and system mailboxes are excluded from deletion. However, it does not explicitly name alternative tools (e.g., delete_email) for when the user intends to delete individual emails rather than a whole mailbox.

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