mailcycle-mcp

mailcycle-mcp

An email address for your AI agent. This MCP server lets an agent read, wait for and reply to mail at its own Mailcycle addresses. Mail is decrypted on the machine running the agent. Mailcycle stores it sealed and can't read it.

Needs a Mailcycle account on Scale or above, and Node 20 or later.

Connect an agent

On the machine the agent runs on:

npx -y mailcycle-mcp pair --name "Support agent"

It prints a line starting with MC1:. In the Mailcycle app, open AI agents, paste the line, and give the agent an email address. The line carries the key that the agent's address keys are sealed with, so keep it private. It goes from your terminal to the app and never through Mailcycle.

Then add the server to your MCP client:

claude mcp add mailcycle -- npx -y mailcycle-mcp

Or in a client's JSON config:

{ "mcpServers": { "mailcycle": { "command": "npx", "args": ["-y", "mailcycle-mcp"] } } }

Added the server before pairing? It still starts, and every tool answers with how to pair. Pair while it runs and the next tool call picks it up, with no restart.

Tools

Tool	What it does
list_addresses	The agent's addresses, and what it may send.
list_messages	The newest messages, with a preview of each.
read_message	One message in full, with its attachments numbered.
read_attachment	Opens an attachment: text as text, images as images, anything else written to a save_to folder.
wait_for_message	Waits for new mail, optionally from a sender or with a subject. Good for sign-up codes and verification links.
reply	Replies to the sender of a message, threaded. Works in reply-only mode. Can attach files by path.
send_message	Sends a new message. Needs the agent set to send to anyone. Can attach files by path.

Sending

Each agent has a send mode, set in the app:

• Reply only (the default): it can answer whoever wrote to it, and no one else.
• Send to anyone: up to 20 messages an hour per agent.
• Read only: it cannot send.

Mail an agent reads can contain instructions written by whoever sent it. Reply only limits what those can make it do. Message bodies are passed to the model marked as the sender's words.

Agents send only from the addresses you assign them, within your plan's daily sending limit.

To send with a name, like "Support at Acme", set Sender name on the address in the app, or on the agent's page for every address it holds. An address's own name wins. The agent picks it up on its next send.

What sees what

• Mailcycle stores mail sealed to keys it doesn't have. Sent mail passes through in plain text and isn't logged. A copy is kept in the address's Sent folder, sealed like received mail.
• This machine holds the agent's key in ~/.config/mailcycle/agent.json, readable only by your user. Anyone with that file can read the agent's mail. Remove the agent in the app to cut it off; the next time it runs, it deletes that file itself.
• Your model provider sees whatever the agent reads.

Options

• mailcycle-mcp status shows the agent's addresses and send mode.
• MAILCYCLE_AGENT_FILE sets where the key is kept, for running more than one agent on a machine.

Licence

Proprietary. Copyright (c) 2026 Northlab Studios Ltd. All rights reserved. You may run this package, unmodified, to connect AI agents to a Mailcycle account you're authorised to use. You may not copy, modify, redistribute or reverse engineer it. See the LICENSE file included with it and the Terms of Service.