JMAP MCP Server

Rust-based MCP server that exposes JMAP email actions over stdio/JSON-RPC. Drop it into any MCP-aware tool to search, manage, and send mail through a JMAP-compatible provider.

Highlights

• Mail search, retrieval, threading, move, delete, and keyword updates
• Mailbox discovery with hierarchy awareness
• Email composition and submission (including reply-all)
• Capability-driven tool registration with JSON Schema metadata
• Single static binary; no runtime dependencies beyond a JMAP server

Quick Start

1. Install the Rust toolchain (1.75+ recommended).

2. Build the binary:

   cargo build --release
   

3. Point your MCP client at the resulting executable, e.g.:

   {
     "mcpServers": {
       "fastmail": {
         "type": "stdio",
         "command": "/home/richard/Projects/rdh-jmap-mcp/target/release/rdh-jmap-mcp",
         "env": {
           "JMAP_SESSION_URL": "https://api.fastmail.com/jmap/session",
           "JMAP_BEARER_TOKEN": "API_TOKEN"
         }
       }
     }
   }
   

Configuration

Variable	Required	Purpose
JMAP_SESSION_URL	Yes	Session discovery endpoint (often /.well-known/jmap)
JMAP_BEARER_TOKEN	Yes	OAuth/Bearer token for API access
JMAP_ACCOUNT_ID	No	Explicit account selection (auto-detected when omitted)

The server inspects the advertised capabilities. Write operations disappear for read-only accounts, and submission tools require urn:ietf:params:jmap:submission.

Available Tools

search_emails, get_emails, get_threads, get_mailboxes, mark_emails, move_emails, delete_emails, send_email, and reply_to_email. Each tool is described through JSON Schema surfaced to the MCP client, including parameter types, bounds, and optional fields.

Architecture

• tokio for async stdio and HTTP
• reqwest for JMAP calls
• schemars for JSON Schema generation
• Rigorous error propagation that mirrors JMAP failure details

Development

cargo run    # start in debug mode
cargo test   # run the Rust test suite

Security Notes

• Validates tool input before issuing requests
• Consumes credentials exclusively from environment variables
• Avoids logging tokens or sensitive payloads
• Adheres to JMAP security guidance

Compatibility

Tested with Stalwart; designed to work with Cyrus IMAP, Fastmail, Apache James, and any other JMAP-compliant implementation.

Contributing

Fork the repo, branch, implement, test, and open a PR. MIT licensed.

References

• Model Context Protocol
• JMAP Core RFC 8620
• JMAP Mail RFC 8621