Documentation

Everything an agent, or the developer behind it, needs to use letterport.

letterport gives an AI agent its own email address. Create an inbox with one API call (or one sentence to an agent connected over MCP); mail sent to it arrives as JSON; the agent replies from the same address, in the same thread, and every email it sends has a delivery trail for each recipient.

Start here

• How to give an AI agent its own email address: the REST API, step by step, in curl and Node.js.
• Give Claude Code an email inbox with MCP: one command, a browser sign-in, then plain words.

Reference

• API reference: every endpoint, with its fields and errors.
• OpenAPI description: the same, machine-readable, for code generators and agents.
• Agent Skill: the API and the mail rules written for a coding agent; install it in Claude Code with one command.
• llms.txt: an index of this site for AI assistants.

How letterport works

Inbox

A real address, name@letterport.dev or on your own domain, that receives mail the moment it exists. A paused inbox keeps receiving and sends nothing. A deleted address is never given out again.

Message

One email, received or sent, as JSON: sender, recipients, subject, text and html, extracted_text, attachments, and the thread it belongs to.

extracted_text

Only what the sender just wrote: the reply without the quoted history below it. What an agent should read to understand a reply.

Thread

A conversation in one inbox. Messages join it by their Message-ID, In-Reply-To and References headers, never by subject, and the agent's replies carry the same headers, so they stay in the other person's conversation too.

Delivery trail

For each recipient of an email you send: queued, sent, then delivered, bounced or complained. Sending answers 202 (queued); "delivered" means the receiving server said so.

Webhook

A signed POST to your endpoint (Standard Webhooks) when mail arrives or a send changes state, retried for about 24 hours. Payloads carry ids; fetch the message over the API.

API key

Permissions read, send and manage, optionally limited to one inbox and given an expiry. MCP connections choose the same permissions when you sign in.

Limits

Sending counts recipients, per day and per month (To, Cc and Bcc each count). Within a minute: 600 requests or 20 recipients. A message is at most 10 MB and 50 recipients; a received email over 25 MB isn't kept. Limits are hard caps: nothing is billed for going over. See pricing.

Help

Write to support@letterport.dev. What is live and what is in early access is listed on the home page.