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jmap-dav-mcp

Generic Model Context Protocol (MCP) server for open email/PIM standards:

• Mail via JMAP (RFC 8620/8621)

• Calendar via CalDAV

• Contacts via CardDAV

Works with any compliant server. Fastmail works out of the box (this project began as fastmail-mcp), and the JMAP side also works with self-hosted servers like Stalwart, Cyrus, and Apache James. The CalDAV/CardDAV side works with iCloud, Nextcloud, Radicale, Baïkal, and friends.

Tool domains (mail / calendar / contacts) are registered based on which credentials you configure — a calendar-only setup exposes only calendar tools.

Requirements

• Bun 1.3+ (recommended) or Node.js 18+

• Credentials for a JMAP and/or CalDAV/CardDAV server

Related MCP server: FastMail MCP Server

Configuration

Mail (JMAP)

Calendar + Contacts (CalDAV/CardDAV)

Domain selection

Fastmail

Legacy FASTMAIL_* variables are fully supported and imply the Fastmail server URLs, so an existing Fastmail setup needs no URL configuration:

• FASTMAIL_USERNAME + FASTMAIL_APP_PASSWORD — mail (JMAP basic auth) + calendar + contacts

• FASTMAIL_API_TOKEN — mail via JMAP bearer token (optional alternative)

• FASTMAIL_BASE_URL, FASTMAIL_CALDAV_URL, FASTMAIL_CARDDAV_URL, FASTMAIL_DAV_USERNAME, FASTMAIL_ORGANIZER_EMAIL — optional overrides

Create an app password in Fastmail Settings → Privacy & Security → App passwords.

Install

bun install

Optional (bundle to dist/):

bun run build

Run

bun run start        # all configured domains

Dev (auto-reload):

bun run dev

Via bunx:

bunx --bun github:adinschmidt/fastmail-mcp

Entry points

MCP Client Config Examples

Fastmail (mcpServers)

{
  "mcpServers": {
    "fastmail": {
      "command": "bun",
      "args": ["/absolute/path/to/jmap-dav-mcp/src/index.ts"],
      "env": {
        "FASTMAIL_USERNAME": "you@fastmail.com",
        "FASTMAIL_APP_PASSWORD": "your-app-password"
      }
    }
  }
}

Generic servers

{
  "mcpServers": {
    "mail-calendar-contacts": {
      "command": "bun",
      "args": ["/absolute/path/to/jmap-dav-mcp/src/index.ts"],
      "env": {
        "JMAP_BASE_URL": "https://mail.example.com",
        "JMAP_API_TOKEN": "your-token",
        "CALDAV_URL": "https://dav.example.com",
        "CARDDAV_URL": "https://dav.example.com",
        "DAV_USERNAME": "you@example.com",
        "DAV_PASSWORD": "your-app-password"
      }
    }
  }
}

Calendar/contacts only (e.g. iCloud, Nextcloud)

{
  "mcpServers": {
    "calendar": {
      "command": "bun",
      "args": ["/absolute/path/to/jmap-dav-mcp/src/bin/dav-mcp.ts"],
      "env": {
        "CALDAV_URL": "https://caldav.icloud.com",
        "CARDDAV_URL": "https://contacts.icloud.com",
        "DAV_USERNAME": "you@icloud.com",
        "DAV_PASSWORD": "app-specific-password"
      }
    }
  }
}

Tools

Mail (JMAP):

• list_mailboxes

• create_mailbox

• update_mailbox

• delete_mailbox

• list_emails

• get_email

• search_emails

• send_email

• mark_email_read

• move_email

• delete_email

• get_email_attachments

• download_attachment

Calendar (CalDAV):

• list_calendars

• create_calendar

• update_calendar

• delete_calendar

• get_calendar_event

• list_calendar_events

• create_calendar_event

• update_calendar_event

• delete_calendar_event

Contacts (CardDAV):

• list_contact_lists

• list_contacts

• get_contact

• create_contact

• search_contacts

• update_contact

• delete_contact

Security Notes

• Prefer app passwords / API tokens over your account password.

• delete_mailbox refuses to delete protected system mailboxes (Inbox, Spam, Trash, Sent, Drafts, Archive).

• delete_calendar refuses to delete the last remaining calendar.

Troubleshooting

403 Forbidden creating calendar events

In almost all cases this means you're trying to write to a read-only calendar (e.g. a subscribed/shared calendar).

1. Run list_calendars

2. Pick a calendar with canWrite: true

3. Use that calendar's id as calendarId for create_calendar_event

JMAP session errors on non-Fastmail servers

The session is discovered at <JMAP_BASE_URL>/.well-known/jmap, following redirects with auth. If your server hosts the session elsewhere, set JMAP_SESSION_URL directly.