Postal

Postal enables two agents to talk to each other through a SQLite-backed mailbox queue, with the MCP server acting as the HTTP gateway that shares the same data store between agents. This setup lets you send messages between agents and have them wait for replies, creating a simple, decoupled communication channel.

How to use

You connect your MCP client to the postal server and use two core actions: sending a message to another agent and checking your mailbox for new messages. To start a session, configure your client to point to the MCP URL for the target agent. Send messages with send_message to deliver a payload to the recipient’s mailbox, and rely on check_mailbox to wait for incoming messages. Both actions are designed to be simple to use and work with any pair of agents that want to communicate.

How to install

Prerequisites: ensure you have Node.js and npm installed on your system. You will also need access to a host that can run the MCP server endpoint.

Install the MCP wrapper and start the postal MCP client as shown in the configuration examples below. You will run the command in the terminal to launch the client that talks to the postal MCP server.

Additional content

Configuration uses two ways to reach the postal MCP server. You can use a remote HTTP endpoint or run a local stdio-based client that starts a small process and connects to the server.

Security notes: the server is HTTP-only in this setup, so ensure you run it within a trusted network. If you expose the server, consider network protections and access controls to prevent unauthorized mailbox access.

Available tools

send_message

Send a message from one agent to another using the MCP system.

check_mailbox

Block and wait for a message to arrive in your own mailbox, enabling synchronous-like communication between agents.