The only thing worse than that is emailing them a simple boolean question and then your phone rings.

Sounds like you should respond to that with a 400 Bad Request

The server cannot or will not process the request due to something that is perceived to be a client error (e.g., malformed request syntax, invalid request message framing, or deceptive request routing).

Valid alternatives: 307 temp redirect to mailbox, 402 payment required to endure such pain or the classic 418. I’d go with the 418.