Ask HN: how to unit/integration test app that sends email?

I'm adding a "register->confirm email->reg. complete" functionality to a web app I'm writing. I'd like to be able to unit/integration test my email-sending code.

I don't want to actually send emails. In fact, I'd like to keep all this local to my machine (or at least to my home network). And if I can avoid it, I don't want to install/configure sendmail/qmail/postfix/etc.; i.e., I don't want to install a real email server.

Is there a test SMTP server anyone knows of that's quick and easy to install (on Linux)? Or a clever hack using honeyd to fake out the SMTP communication?