The one that lets you automate without losing control. Before plugging an AI into your contacts, check:
- approval before sending, when you want it;
- automatic sending set assistant by assistant, with a daily cap;
- stopping all sends in one click;
- connection through OAuth, with no key to copy;
- a log of what the assistant did;
- where your data is.
The details, and Mailpro's answer on each point: the 8 criteria for choosing an MCP server.