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Set-up documentation

Connect your mailbox to the Claude desktop app

The Claude desktop app takes a remote MCP server through the same Connectors screen as the web. No JSON file, no npx bridge, no local install.

Time About 2 minutes
Where Settings, then Connectors, then Add custom connector
It needs URL only, then sign in

You do not need the JSON file

If you have searched for how to add an MCP server to the Claude desktop app, most of what you found will have told you to edit a file called claude_desktop_config.json, install something with npx, and restart the app. Ignore all of it. None of it applies here.

That advice describes a local MCP server: a program that runs on your own machine and that Claude launches and talks to over its standard input and output. It was the only kind the desktop app could hold when MCP first shipped, which is why the search results are still full of it. This is a remote server, which is a URL, and the desktop app takes one through the same Connectors screen the web does.

What that saves you

No file to find, no Node installation, no bridge process sitting in your menu bar, and nothing to update when the server changes. It also means your phone and the web app get the same connector without doing anything twice, because it is attached to your Claude account rather than to this computer.

The longer version of that distinction, and how to tell which kind any given server is, is in remote and local MCP servers.

Add the connector

  1. Open Settings, then Connectors

    From the app's own settings, not from a file. If you are signed in to the same account on the web, anything you have already added there is in this list, and vice versa.

  2. Choose Add custom connector

    Name it after the mailbox. It is free text, so use the address or something you will recognise: "work mail" beats "mailbox-mcp" when you are choosing between two of them in a hurry.

  3. Paste the connector URL

    Connector URL The same for every account 
    https://mcp.mailbox-mcp.com/db/mcp/YOUR-MAILBOX-KEY

    Leave the advanced OAuth boxes empty. This server registers its own client, so there is no client ID to find and no secret to paste, and filling them in is the most common way this goes wrong. The Claude.ai page explains that in full.

  4. Press Connect and sign in

    Your default browser opens on the control panel. Sign in, choose which mailbox this connector should open, and you are handed back to the desktop app with the tools attached.

Check that it worked

Start a new conversation. The tools do not announce themselves, so ask for something you can check against your own mailbox without leaving the window.

Try this first

Find the last three emails from anyone at my own domain and tell me what each one was about.

A search rather than a listing, so it exercises the part most likely to be misconfigured. Nothing is marked read by asking: reading through this server never sets the seen flag.

If something goes wrong

  • Symptom

    The browser opened and nothing came back

    The desktop app is waiting for the browser to hand it back. If you signed in on a different browser profile from the one that opened, or the window was closed before the panel finished, remove the connector and add it again.

  • Symptom

    It works on the web but not on the desktop

    Check you are signed in to the same Claude account in both. Connectors belong to the account, so a connector that is present in one and missing in the other is two accounts rather than a broken connector.

  • Symptom

    You edited claude_desktop_config.json and now nothing works

    Undo it. A remote server does not belong in that file, and a malformed entry there can stop the app loading any MCP server at all, including the ones you added properly through Connectors.

The free tier is 5 MCP calls a day on any mailbox, with no card. Enough to connect a mailbox and see it answer in the desktop app.

Connect a mailbox Sign in

Where to go next

Claude.ai is the same connector on the same account, so this is already done there. Claude Code is a separate one command, because the terminal keeps its own configuration.

The use cases cover what is worth asking for once it is attached, and the tool reference lists every tool and marks the read-only ones.

Read 30 August 2026 Verified against a live connector on that day. If it has changed since, tell us and we will read it again.

By Mark McNeece, Founder Published Last reviewed Editorial standards