MCP + Claude Desktop not working

Help
1

Downloaded and installed the latest Mailspring. Saw in the release notes about MCP integration and got very excited. I enabled the MCP server, added to Claude Desktop, went over to Claude to try it and … failed.

Error log below:

2026-07-24T18:11:51.513Z [mailspring] [info] Initializing server... { metadata: undefined }
2026-07-24T18:11:51.526Z [mailspring] [info] Using MCP server command: /Applications/ServBay/script/alias/npx with path: {
  metadata: {
    paths: [
      '/Users/Treehouse103/.local/bin',
      '/Applications/ServBay/script/alias',
      '/Applications/ServBay/bin',
      '/Applications/ServBay/sbin',
      '/Applications/ServBay/script',
      '/Applications/ServBay/package/python/current/Python.framework/Versions/Current/bin',
      '/Applications/ServBay/package/node/current/bin',
      '/Applications/ServBay/package/go/current/bin',
      '/Applications/ServBay/package/openjdk/current/bin',
      '/Applications/ServBay/package/rust/current/bin',
      '/Applications/ServBay/package/ruby/current/bin',
      '/Applications/ServBay/package/dotnetsdk/current',
      '/Applications/ServBay/package/dotnetsdk/current/tools',
      '/Users/Treehouse103/.dotnet/tools',
      '/Applications/ServBay/package/mono/current',
      '/opt/homebrew/bin',
      '/opt/homebrew/sbin',
      '/usr/local/bin',
      '/System/Cryptexes/App/usr/bin',
      '/usr/bin',
      '/bin',
      '/usr/sbin',
      '/sbin',
      '/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin',
      '/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin',
      '/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin',
      '//Applications/Topaz Photo AI.app/Contents/Resources/bin',
      '/Users/Treehouse103/.cargo/bin',
      [length]: 28
    ]
  }
} %o
2026-07-24T18:11:51.528Z [mailspring] [info] Server started and connected successfully { metadata: undefined }
Error: Node.js executable for command 'npx' could not be found.
Checked ServBay (project config: '', default), NVM (NVM_BIN: '', alias/default), Homebrew, and system paths.
2026-07-24T18:11:51.570Z [mailspring] [info] Server transport closed { metadata: undefined }
2026-07-24T18:11:51.570Z [mailspring] [info] Server transport closed unexpectedly, this is likely due to the process exiting early. If you are developing this MCP server you can add output to stderr (i.e. `console.error('...')` in JavaScript, `print('...', file=sys.stderr)` in python) and it will appear in this log. { metadata: undefined }
2026-07-24T18:11:51.570Z [mailspring] [error] Server disconnected. For troubleshooting guidance, please visit our [debugging documentation](https://modelcontextprotocol.io/docs/tools/debugging) { metadata: { context: 'connection', stack: undefined } }
2026-07-24T18:11:51.570Z [mailspring] [info] Client transport closed { metadata: undefined }
2026-07-24T18:11:51.570Z [mailspring] [info] Client transport closed { metadata: undefined }
2

Thanks for trying this out! The “Add to Claude Desktop” button registers Mailspring’s MCP server in Claude’s config using the bare command npx, trusting it’s on Claude Desktop’s PATH when it launches. Your log shows Claude Desktop’s own Node resolver isn’t finding npx, which lines up with having Node installed through ServBay rather than a location Claude Desktop’s launcher checks (like Homebrew or nvm).

Quick fix: open Terminal, run which npx to get the full path, then open ~/Library/Application Support/Claude/claude_desktop_config.json and replace "command": "npx" under the mailspring entry with that full path. Installing Node via nvm or Homebrew and re-clicking “Add to Claude Desktop” should also work.

I’ll look at having Mailspring write the resolved path directly instead of the bare command, since this’ll trip up more people with non-standard Node installs.