MailStream for ChatGPT

app.mailstream/mailstream

The first MCP server for physical mail: send postcards and letters, manage lists and campaigns.

client:ChatGPT transport:streamable-http

Install MailStream in ChatGPT

Settings → Connectors → Advanced → Developer mode

https://my.mailstream.app/mcp

Custom connectors are a paid-plan feature and take a remote URL only. ChatGPT cannot run a packaged server locally. ChatGPT docs