Edit: Someone1234: you don't need to wait for companies to support my proposal. It already works today with Gmail: try my live demo on pm33at@gmail.com - it works by leveraging standard auto-responder features. As to the comparison with XKCD 927, it is invalid: my proposal is radically different from anything that currently exists, because it is decentralized while all current personal information sharing platforms are centralized.
Edit: rakoo: yes, XMPP would work too, and would probably be a bit better than SMTP because it is real time. However in practice building something over SMTP has more chances of seeing success (because not everybody uses XMPP, but everybody has email).