Have ChatGPT or Claude send a postal letter

Ask ChatGPT or Claude to write a cancellation letter: it does it in seconds. Ask it to send it: it tells you it can't. Assistants can write, but they don't have a letterbox. A tool is missing, and that's exactly what an MCP server provides.

What an MCP server is

MCP (Model Context Protocol) is a standard way to give tools to an AI assistant. You connect an MCP server to your assistant, like an extension, and the assistant can then use it when the conversation calls for it: look something up, act in a service, or here, post a letter.

ChatGPT, Claude, Grok, Mistral's Le Chat, and editors such as VS Code or Cursor can connect to a remote MCP server from a simple URL.

What the assistant does with Cachet

Cachet gives the assistant seven tools:

• check_address checks an address and formats it to La Poste's standard, using the Base Adresse Nationale (France's national address database);
• quote gives the price of a letter, printing and stamp included;
• prepare_letter lays out the letter and returns a preview to show you;
• send_letter sends the letter you approved, and returns a payment link (or pays from your prepaid balance if it's enough);
• track_letter tracks the letter: posting, delivery, delivery receipt;
• get_balance gives your prepaid balance;
• add_funds tops it up by €50 or €100: approved letters are then paid from it, up to €0.30 cheaper and without a link.

The letter is printed, put in an envelope and handed to La Poste, the French postal service, as an ordinary letter, a tracked letter or a lettre recommandée avec accusé de réception (registered letter with proof of delivery), anywhere in France, overseas territories included. Count from €3.87 for a one-page ordinary letter and from €9.99 for a registered letter with proof of delivery.

Connecting it, step by step

1. Copy the server URL: https://www.taraxe.com/cachet/mcp.
2. In your assistant (ChatGPT, Claude, Grok or Le Chat), open the connectors page and add a custom connector with that URL. In ChatGPT, you sometimes have to turn on developer mode first. The Cachet page gives the exact path for each assistant, and a one-click install link for VS Code and Cursor.
3. The first time, sign in with your email: a code is enough, no password. Your letters are tied to that account.
4. Ask for a letter, for example: “Prepare a registered letter to cancel my gym membership.”

What happens next

The assistant asks for whatever is missing (your address, the recipient's, the contract number), then writes the letter, in French when the recipient is French. It checks the address and shows you the exact preview of the letter, with its price. If you agree, it gives you a payment link: card, Apple Pay or Google Pay. The letter goes out once paid. Paid before 5 pm on a working day, it's handed to La Poste the same day.

After that, the assistant can track the letter when you ask: the tracking number, the proof of posting, then the signed delivery receipt for a registered letter.

The safeguards

An assistant that posts mail in your name deserves clear limits. Cachet's:

• Nothing goes out without you. The send tool requires the exact preview to have been shown and approved, and you pay for each letter yourself, through a link.
• No anonymous mail. Every letter carries its sender's name and address.
• No bulk mail. Sending is capped each day: Cachet handles the paperwork of one person or one company, not mailing campaigns.
• A test mode. With test_mode: true, the assistant goes through the whole flow without posting or paying anything.

For other actions an agent shouldn't decide alone (paying an invoice, sending an email, deleting something), Aval lets it ask you the question on your phone and wait for your answer.

Which letters?

All the ones that still need paper, and that you keep putting off because you have to print, find an envelope and go to the post office: a cancellation, a mise en demeure (formal notice), a reminder for an unpaid invoice, a dispute. The guide ordinary, tracked or registered letter helps you choose how to send it.

Frequently asked questions