Send a letter from Claude, Cursor, or Codex

Here's something your coding agent can do that it probably hasn't tried: put a physical letter in the mail. One MCP server — mailsnail — adds tools for real USPS mail. Nothing to install: you add a URL and sign in, the same as connecting any other account. Below is the exact setup for the clients most people run, then a 60-second "mail me a letter" walkthrough.

The source of truth for every client config is mailsnail.dev/setup — copy from there if a snippet here ever drifts.

Claude Code

One command:

claude mcp add -t http mailsnail https://api.mailsnail.dev/mcp

Then run /mcp, select mailsnail, and choose Authenticate. Your browser opens our sign-in page; approve it and the tools appear on the next turn.

Worth knowing: adding the server does not pop the browser by itself. If nothing happened after that command, nothing is broken — you just haven't started the sign-in yet.

Claude Desktop

Settings → Connectors → Add custom connector, and paste:

https://api.mailsnail.dev/mcp

Claude Desktop registers itself with our sign-in server automatically, so there's no client ID to create. Approve the connection in the browser and the mail tools appear under the connectors icon.

Cursor

Add the URL form to .cursor/mcp.json (project) or ~/.cursor/mcp.json (global):

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

Cursor prompts you to sign in the first time the server is used.

Codex CLI

Codex reads MCP servers from ~/.codex/config.toml and launches them as local processes, so this one runs the package rather than the hosted server. You supply your own Click2Mail or Lob credentials:

[mcp_servers.mailsnail]
command = "npx"
args = ["-y", "mailsnail"]

[mcp_servers.mailsnail.env]
MAIL_PROVIDER = "click2mail"
CLICK2MAIL_USERNAME = "your-username"
CLICK2MAIL_PASSWORD = "your-password"

The magic moment: mail yourself a letter

Once it's wired in, try this prompt verbatim:

Use mailsnail to send a letter to [your address] that says "my agent mailed this."

Watch what the agent does:

1. verify_address confirms your address is deliverable before spending anything.
2. preview_letter renders the piece and returns the exact price — from $1.21 for a one-page, black-and-white letter from a balance ($1.51 if you pay for just that letter by card), still nothing charged.
3. It shows you the preview and the price, and — if you've set it up that way — waits for your go-ahead.
4. send_letter mails it and hands back a tracking id.

Certified mail is the same flow with one flag, from $8.61 from a balance ($8.83 for one letter by card), with tracking. Everything is priced at our cost, and the preview shows the exact prices for your piece. Mail is paid for from a prepaid balance you fund through Stripe, or one letter at a time by card — if the balance is empty, the first send hands back two links: one to pay for just that letter, one to add funds to your balance. Both are one-time payments. Your card isn't saved unless you opt in to auto-reload, and you can turn that off any time. A piece that fails to mail is refunded automatically.

Related guides

• How to send physical mail from an AI agent — the concepts, the tools, and what it costs.
• How to send a real letter from ChatGPT — the same setup in ChatGPT.
• Certified mail with a return receipt from an AI agent — for notices that need proof.
• A Lob / PostGrid alternative built for agents — coming from an incumbent mail API.

claude mcp add -t http mailsnail https://api.mailsnail.dev/mcp

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