Send Letters from Cursor

Setup

Add Mailsnail to ~/.cursor/mcp.json (or your project's .cursor/mcp.json):

{
  "mcpServers": {
    "mailsnail": {
      "url": "https://api.mailsnail.dev/mcp"
    }
  }
}

Cursor prompts you to sign in the first time the server is used. Approve it in the browser and the agent has send_letter and friends available. Nothing to install and no API key.

What this enables

• Customer success workflows where an agent drafts a piece of mail in response to an event in your codebase (a closed support ticket, a successful onboarding milestone).
• Personal assistant flows: ask Cursor to mail a thank-you note based on a meeting transcript in your repo.
• Onboarding kits: Cursor watches for a new user signup in your test data and the agent mails them a welcome letter.

Tips

• Keep recipient addresses in a small JSON file the agent can read. Your prompts get shorter and the agent's tool calls get more reliable.
• For multi-piece flows, have the agent write each receipt_token from send_letter to a log file, and check it before queuing more. get_letter on a token tells you where that piece is.
• Keep send_letter behind Cursor's tool-approval prompt. preview_letter is free, so the agent can show you the proof and price first.

Full setup walkthrough: /setup. Tool reference: /llms-full.txt.