Fastmail Blade MCP

The only MCP server built on Fastmail's native JMAP protocol — email, masked email, and push notifications with token-efficient output.

Wraps the Fastmail JMAP API via jmapc as an MCP server using FastMCP 2.0.

Why Fastmail Blade?

Every other email MCP uses IMAP — a 1986 protocol that was never designed for programmatic access. Fastmail Blade uses JMAP, Fastmail's native protocol:

• JMAP-native — stateless, JSON-based, supports batch operations natively. No IDLE hacks, no MIME parsing, no connection state management.
• Masked Email — full CRUD for Fastmail's privacy aliases (create, list, enable/disable). No IMAP MCP can touch this — it's a Fastmail extension that only exists in JMAP.
• Push notifications — real-time EventSource via JMAP Push. Know when mail arrives without polling.
• Incremental sync — JMAP state tokens for delta changes. Get only what's new since your last check, not the entire mailbox.
• Token-efficient — concise pipe-delimited output, null-field omission. IMAP MCPs dump raw headers and MIME multipart.
• Write-safe — env-gated writes, batch limits (50 max), credential scrubbing on all error paths.

Features

• 18 tools: email read/write/manage, masked email, push notifications, meta
• Masked Email management — no other MCP server exposes this Fastmail extension
• JMAP Push (EventSource) — real-time state change notifications
• Write-gate — all write operations disabled by default (FASTMAIL_WRITE_ENABLED=true)
• Token-efficient — concise output, capped lists, null-field omission
• Batch limits — mail_bulk capped at 50, mail_search defaults to 20
• SKILL.md — self-teaching instructions for Claude

Requirements

• macOS (tested) or Linux
• Python 3.12+
• uv
• Fastmail account with API token

Quick Start

# Clone and install
cd fastmail-blade-mcp
uv sync

# Set your API token
export FASTMAIL_API_TOKEN=fmu1-xxxxxxxx

# Run (stdio transport)
uv run fastmail-blade-mcp

Claude Code

claude mcp add fastmail-blade -- uv run --directory ~/src/fastmail-blade-mcp fastmail-blade-mcp

Claude Desktop (claude_desktop_config.json)

{
  "mcpServers": {
    "fastmail-blade": {
      "command": "uv",
      "args": ["run", "--directory", "/path/to/fastmail-blade-mcp", "fastmail-blade-mcp"],
      "env": {
        "FASTMAIL_API_TOKEN": "fmu1-xxxxxxxx",
        "FASTMAIL_WRITE_ENABLED": "false"
      }
    }
  }
}

Tools (18)

Email Read (5)

Tool	Description
mail_mailboxes	Mailbox list with ID, name, total/unread, role
mail_read	Full email: headers + body
mail_search	Search with filters (sender, subject, date, mailbox, keywords)
mail_threads	Chronological conversation view
mail_snippets	Search with highlighted context excerpts

Email State & Sync (2)

Tool	Description
mail_state	Get JMAP state token for change tracking
mail_changes	Incremental changes since a previous state token

Email Write (4, gated)

Tool	Description
mail_send	Send new email
mail_reply	Reply (preserves threading)
mail_move	Move to mailbox
mail_flag	Set/clear keywords ($flagged, $seen, etc.)

Email Manage (2, gated)

Tool	Description
mail_delete	Move to Trash (default) or permanently destroy
mail_bulk	Bulk action on up to 50 emails

Masked Email (3)

Tool	Description
masked_list	List aliases with state, domain, description
masked_create	Create new masked alias (gated)
masked_update	Update state/description (gated)

Push (2)

Tool	Description
push_subscribe	Listen for state changes via EventSource
push_status	Check EventSource availability

Security

Layer	Control
Secrets	FASTMAIL_API_TOKEN from env (never logged)
Transport	stdio default (no network exposure)
Write gate	FASTMAIL_WRITE_ENABLED default false
Batch limits	mail_bulk capped at 50
Token scrubbing	API token removed from all error output
HTTP auth	Optional bearer token middleware

HTTP Transport

export FASTMAIL_MCP_TRANSPORT=http
export FASTMAIL_MCP_HOST=127.0.0.1
export FASTMAIL_MCP_PORT=8767
export FASTMAIL_MCP_API_TOKEN=your-secret-token

uv run fastmail-blade-mcp

Environment Variables

Variable	Default	Description
FASTMAIL_API_TOKEN	(required)	Fastmail API token
FASTMAIL_WRITE_ENABLED	false	Enable write operations
FASTMAIL_MCP_TRANSPORT	stdio	Transport: stdio or http
FASTMAIL_MCP_HOST	127.0.0.1	HTTP bind host
FASTMAIL_MCP_PORT	8767	HTTP bind port
FASTMAIL_MCP_API_TOKEN	(none)	Bearer token for HTTP auth

Architecture

src/fastmail_blade_mcp/
├── server.py       — FastMCP 2.0 server, 18 @mcp.tool decorators
├── client.py       — JMAP client via jmapc, masked email, push subscriptions
├── formatters.py   — Token-efficient output (pipe-delimited, null omission)
├── models.py       — Config, write-gate, batch limits
└── auth.py         — Bearer token middleware for HTTP transport

Built with FastMCP 2.0 and jmapc.

Development

make install-dev    # Install with dev dependencies
make test           # Run unit tests (92 tests, mocked)
make test-e2e       # Run E2E tests (requires live Fastmail)
make check          # Lint + format + type-check
make run            # Start the server

License

MIT