Sometimes I think HN users live in a bubble. Although the OP seems very aware of this, many of you think this is some fancy new idea.

http://en.wikipedia.org/wiki/Disposable_e-mail_address

Going back even further, to the 90's, it looks like tempalias is just a no-account version of http://mailexpire.com

My advice to the OP, now that you have your proof of concept, is get the heck out, running a disposable email address service is a nightmare. Welcome to a world of spammers, blocklists, backscatter, exploiters, calls from police, etc.