How to send physical mail from an AI agent

Your agent can already send an email, call an API, open a browser, and write code. The one channel it couldn't reach was the oldest one — a stamped envelope in someone's mailbox. Mailsnail closes that gap. It's an MCP server, so any agent that speaks the protocol — Claude Code, Claude Desktop, Cursor, Codex, the OpenAI Agents SDK — can send a real, postmarked USPS letter, postcard, or certified piece with a single tool call.

No account. No API keys. The agent pays per piece.

The 30-second version

claude mcp add mailsnail -- npx -y mailsnail

That's the whole install. Ask your agent to mail a postcard, and it will — routing through seven tools it now has:

• verify_address — check an address is deliverable (USPS CASS) before you spend a cent
• preview_letter — render the exact piece and return the exact price, nothing charged
• send_letter — mail a first-class or certified letter
• send_postcard — mail a 4×6 postcard
• get_letter / list_letters — check status and history
• cancel_letter — pull a piece back before it hits production

What it costs

Flat and public, so an agent can reason about the price before it commits:

• First-class letter — $1.50
• Certified mail — $9.00
• Postcard — $1.00

preview_letter returns that number with nothing charged. The agent decides whether the send is worth it and — if you've wired it that way — checks with you first.

How "no signup" actually works

This is the part people don't expect. Most mail APIs make you create an account, add a card, and provision keys before the first send. Mailsnail doesn't. Payment happens per piece, at the moment of the call, over the Machine Payments Protocol (HTTP 402) using a Stripe Shared Payment Token — the agent spends inside the wallet you authorized, and nowhere else. If a piece fails to mail, the charge is refunded automatically. (USDC/x402 settlement is coming, for agents that would rather pay in stablecoin.)

The upshot is simple: the gap between "install" and "a letter is in the mail" is minutes, not a procurement cycle.

What you'd actually use it for

Not bulk marketing blasts. The pieces that fit are low-volume and high-intent — the ones never worth standing up a print vendor for:

• A thank-you note mailed after a support ticket is resolved well
• A welcome kit when someone signs a contract
• Preliminary lien notices and other compliance mail that legally has to be physical and postmarked
• Condolence or birthday cards a personal-assistant agent sends without being reminded
• One personalized letter to one account when a trigger fires, written by the agent that has the context

Send your first piece

1. Install — claude mcp add mailsnail -- npx -y mailsnail
2. Ask — tell your agent to mail a postcard to a specific address
3. It verifies — verify_address confirms the address is deliverable
4. It previews — preview_letter returns the rendered piece and the exact price, still $0 charged
5. It sends — on your go-ahead, send_letter / send_postcard mails it and returns a tracking id
6. You check — get_letter shows status; cancel_letter works until it's in production

Related guides

• Send a letter from Claude, Cursor, or Codex — the exact per-client setup.
• A Lob / PostGrid alternative built for agents — if you're moving off an incumbent mail API.

{
  "mcpServers": {
    "mailsnail": {
      "command": "npx",
      "args": [
        "-y",
        "mailsnail"
      ],
      "env": {
        "MAIL_PROVIDER": "managed",
        "MAIL_API_BASE_URL": "https://api.mailsnail.dev"
      }
    }
  }
}