Developers

Send as hello@ — from your app or your agent.

MailerZ API and MCP share one workspace key, so you can send as a custom domain you host. Mint that key on the desk. POST /api/v1/send for apps. POST /api/mcp for Claude, Cursor, Hermes, Cline, Continue, Windsurf, VS Code, and ChatGPT actions. From must be an address you host. We never rewrite header From. We do not accept mail for names we do not host.

Start free — one domain Open Developer

Two doors. Same key. Same gates.

REST send

Apps post JSON to https://mail.mailerz.net/api/v1/send. Bearer mz_live_. Desk login JWTs are rejected.

Send API fields and errors

Key takeaways

  • MailerZ API and MCP use one mz_live_ key. Desk login JWTs are rejected.
  • Send as a custom domain you host. Free plan returns SEND_AS_LOCKED.
  • Cursor, Claude, and Hermes share the same SPF, DKIM, and alias gates as the send API.

What you need before a send succeeds

Paid send-as

A paid plan with send-as on. Free returns SEND_AS_LOCKED.

Your domain

A verified domain you host. Not an open relay.

SPF and DKIM

Live SPF and DKIM.

Enabled alias

An enabled alias such as hello@. Catch-all * is not a From.

Envelope mail is rewritten with SRS. Header From is never rewritten. Limits and scan rules are the same for REST and MCP. See pricing and security. Protocol spec: Model Context Protocol.

Minimal send

curl — POST /api/v1/send
curl -X POST https://mail.mailerz.net/api/v1/send \
  -H "Authorization: Bearer mz_live_YOUR_KEY" \
  -H "Content-Type: application/json; charset=utf-8" \
  -d '{"from":"hello@your-domain.com","to":"user@gmail.com","subject":"Hello","text":"Plain body"}'

Minimal MCP handshake

initialize
{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-03-26","capabilities":{},"clientInfo":{"name":"demo","version":"1"}}}
notifications/initialized
{"jsonrpc":"2.0","method":"notifications/initialized"}
tools/call mailerz_whoami
{"jsonrpc":"2.0","id":3,"method":"tools/call","params":{"name":"mailerz_whoami","arguments":{}}}

Questions

What is MailerZ MCP?

A JSON-RPC 2.0 server on the MailerZ API. Agents call the same send, mailbox, and block tools the desk uses.

Do I need a special MCP key?

No. Use the Send API key from desk → Developer. mz_live_ for a workspace. mz_root_ is operator-only.

Does this work with Claude / Cursor / Hermes?

Yes. Cursor and Hermes can POST HTTP to /api/mcp. Claude Desktop and other stdio clients use npm run mcp as a proxy.

Can the agent create a domain or change my plan?

No.

Can I send on the Free plan?

No. Upgrade so send-as is on, then publish SPF + DKIM.

Do you train on my mail?

No.

Are you an official Anthropic or OpenAI plugin?

No. Any client that speaks MCP JSON-RPC or stdio can connect.

Where do I mint a key?

Register or sign in on the desk, then Developer → API Key.

Mint the key on the desk.

Start free with one domain. After the account exists, open Developer and copy mz_live_.

Start free — one domain Open Developer