I like the proposal, but rather than using special (unfriendly) subjects, I'd use custom email headers. eg: X-Autorespond: name, age, location

Why? So that clients that do not support this protocol will display a normal email to the end-user, instead of something not-so-friendly.

This also means that the body can be free-formed text explaining to the user what this message represents, and how to support this protocol.