Ask an AI assistant whether an email address is real and it will answer confidently. But without a tool it can't look up the domain's mail servers or ask the mailbox whether it exists. It can only judge whether the address looks plausible, which is exactly how typos and dead mailboxes slip through.

The fix is to give the assistant a real tool. With the Model Context Protocol (MCP), Claude, Cursor and other clients can call an email verifier directly, and you get answers backed by DNS and SMTP instead of pattern matching.

Here's how to set that up in a couple of minutes, and the one design rule I think every paid MCP tool should follow.…