Which integrations are available for this server?

Supports Mermaid diagrams for visualizing agent communication flows between systems Available as a package on PyPI for easy installation and distribution Uses SQLite as the backend database for the message queue system between agents

How do I use Postal MCP Server?

1. Click on "Install Server". 2. Wait a few minutes for the server to deploy. Once ready, it will show a "Started" state. 3. In the chat, type @ followed by the MCP server name and your instructions, e.g., "@Postal MCP Server send a message to gemini asking for the test results" That's it! The server will respond to your query, and you can continue using it as needed. Here is a step-by-step guide with screenshots.

Postal: Agent Comms via MCP

PyPI version

A mailbox system for letting two agents talk to each other.

Here's Claude telling gemini how to write unit tests:

Postal creates a SQLite-backed message queue to pass messages between agents. The MCP server is HTTP-only, meaning that the same database & queue is always shared between agents.

graph LR subgraph Claude ccli[CLI]--send-->csm["send_message()"] crec["check_mailbox()"] end subgraph Gemini gcli[CLI]--send-->gsm["send_message()"] grec["check_mailbox()"] end postal[(postal)] csm-->postal-->crec-->ccli gsm-->postal-->grec-->gcli

Postal provides a simple queue, based on SQLite.

Two MCP tools:

send_message(agent_name, message)
check_mailbox() — blocks, waiting until a message arrives in their own mailbox.

Agents can freely send messages to each other.

PROMPT="Notice that you have two tools, check_mail and send_to_agent. You should get **all** instructions from check_mail. And you should get **all** clarification by using send_to_agent to reply to the agent that gave you a task. Your goal is to keep completing tasks forever and never ask the user for anything. Only talk to agents. You are gemini" gemini --yolo --prompt "$PROMPT"

MCP config

It's served as streamable HTTP. The path is in the format /agents/{name}/mcp/.

STDIO example:

{ "mcpServers": { "postal": { "command": "npx", "args": ["-y", "mcp-remote", "http://0.0.0.0:7777/agents/gemini/mcp", "--allow-http", "--transport", "http-only"] } } }

Directly as HTTP:

{ "mcpServers": { "postal": { "url": "http://0.0.0.0:7777/agents/gemini/mcp", "transport": "http" } } }

There's some differences for how "http" is specified. Sometimes it's "streamable-http". Sometimes the key is called "type":.