Fastmail MCP Server (Unofficial)

Unofficial Model Context Protocol server for Fastmail integration. Exposes a single execute tool that acts as a validated JMAP proxy — the LLM writes raw JMAP method calls, and the server handles validation, authentication, and response cleaning.

Setup Instructions

1. Get Your Fastmail API Token

1. Log in to Fastmail

2. Go to Settings → Privacy & Security → API tokens

3. Click New API token

4. Give it a name (e.g., "Claude MCP")

5. Select the required scopes: Mail (read/write as needed)

6. Copy the generated token

2. Configure Claude Code

Add the following to your Claude Code MCP settings (~/.claude/claude_desktop_config.json or project .mcp.json):

{
  "mcpServers": {
    "fastmail": {
      "type": "url",
      "url": "https://fastmail-mcp.vercel.app/mcp",
      "headers": {
        "Authorization": "Bearer YOUR_FASTMAIL_API_TOKEN"
      }
    }
  }
}

Security Note: Keep your API token secure. Never commit it to version control. Consider using environment variables or a secrets manager.

Available Tools

execute

Execute JMAP method calls against Fastmail. Accepts an array of JMAP method call triples [methodName, args, callId].

Input:

{
  "methodCalls": [
    ["Email/query", {
      "filter": { "inMailbox": "INBOX_ID" },
      "sort": [{ "property": "receivedAt", "isAscending": false }],
      "limit": 10
    }, "call-0"],
    ["Email/get", {
      "ids": { "resultOf": "call-0", "name": "Email/query", "path": "/ids" },
      "properties": ["from", "subject", "receivedAt", "preview"]
    }, "call-1"]
  ]
}

What the server does:

• Validates structure, method names, and hygiene rules

• Injects accountId automatically

• Sends to Fastmail's JMAP API

• Strips protocol noise (state, queryState, canCalculateChanges, etc.)

• Returns cleaned methodResponses

Allowed JMAP methods:

• Core/echo

• Mailbox/get, Mailbox/query, Mailbox/queryChanges, Mailbox/set

• Email/get, Email/query, Email/queryChanges, Email/set

• Thread/get

• SearchSnippet/get

• Identity/get

• EmailSubmission/get, EmailSubmission/query, EmailSubmission/set

Validation rules:

• Every /get call (except Mailbox/get, Identity/get) must include a properties array

• Every /query call must include a limit

• ids: null on /get calls is rejected (use /query first)

• Destructive operations (destroy, EmailSubmission/set) return an error asking for user confirmation

API Endpoints

• POST /mcp - MCP protocol endpoint

• GET /health - Health check endpoint

Development

pnpm install   # Install dependencies
pnpm build     # Build for production
pnpm start     # Run local server
pnpm check     # Run all checks (typecheck + lint + fmt + test)
pnpm deploy    # Deploy to Vercel

This is an unofficial community project and is not affiliated with Fastmail.

Source code and issues: GitHub