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AI apps over MCP

Apps that take an MCP server, such as Claude Code, Claude Desktop, Cursor or Codex, can work with your mail through Kestrel: search and read it, mark it done, star and label it, set reminders, list your calendar and write drafts. They use the accounts you have in Kestrel, on this Mac, and talk to Kestrel directly. Nothing goes through a server of ours.

They never send anything. A draft an AI app writes waits in your Drafts until you send it from Kestrel.

Turning it on

The MCP server is off until you turn it on in Settings › Advanced › MCP Server. While it is on, any program running as you on this Mac can read and triage your mail through it without asking, the same way you can. Turn it off again when you don't need it.

The AI app starts Kestrel's server itself when it needs it, so you don't run anything. If Kestrel is closed, the first request opens it in the background, which takes a few seconds.

Adding it to an app

The server is the kestrel-mcp command inside Kestrel. Settings › Advanced › MCP Server shows it with the path of your copy and a button to copy it. With Kestrel in Applications, it is:

/Applications/Kestrel.app/Contents/MacOS/kestrel-mcp

Claude Code:

claude mcp add --scope user kestrel -- /Applications/Kestrel.app/Contents/MacOS/kestrel-mcp

Codex (Codex in the ChatGPT desktop app and the Codex extension for VS Code read the same settings):

codex mcp add kestrel -- /Applications/Kestrel.app/Contents/MacOS/kestrel-mcp

Gemini CLI:

gemini mcp add -s user kestrel /Applications/Kestrel.app/Contents/MacOS/kestrel-mcp

VS Code with GitHub Copilot:

code --add-mcp '{"name":"kestrel","command":"/Applications/Kestrel.app/Contents/MacOS/kestrel-mcp"}'

Claude Desktop, Cursor and LM Studio read a settings file instead. In Claude Desktop, open it from Settings › Developer › Edit Config; Cursor keeps it in ~/.cursor/mcp.json. Add Kestrel, then quit and reopen the app:

{
  "mcpServers": {
    "kestrel": {
      "command": "/Applications/Kestrel.app/Contents/MacOS/kestrel-mcp"
    }
  }
}

ChatGPT on the web reaches only servers on the internet, so it cannot use Kestrel.

What an AI app can do

Tool What it does
accounts, mailboxes Your accounts, and each one's split inboxes, folders and labels.
list Conversations in a mailbox or split inbox, newest first.
search Gmail's search syntax (from:, has:attachment, newer_than:7d…), on the server and on this Mac, for every kind of account.
read A conversation's messages as text. Reading it this way doesn't mark it read.
mark_done, star, mark_read, trash, label Triage, as E, S, U, # and L do.
remind Remind Me (H): "tomorrow", "monday", "2d", "dec 5 3pm", optionally only if nobody replies.
draft A new message or a reply, saved in Drafts. It can open the draft in Kestrel for you to finish.
open Shows a conversation in Kestrel's window.
events Calendar events for a range of days (Gmail accounts).

Each change appears in Kestrel as a toast naming the app that made it, such as "Claude Code: Marked done (3)", and Z undoes it like any other change.

The app is told that the text of your mail is written by other people: it treats it as information, never as instructions, and it asks you before changing anything you didn't ask it to change. Still, check what it proposes before you agree to it.

When it doesn't answer

  • "Kestrel's MCP server is off": turn on Settings › Advanced › MCP Server.
  • "Another copy of Kestrel is already answering": two copies of Kestrel are open. Quit one, then turn the setting off and on again.
  • After you move Kestrel to another folder, update the path in the AI app's settings.