Users not receiving registration e-mail

My friend sent me an IM a while ago telling me that he had tried to register for my site but hadn’t received a verification e-mail and couldn’t log in. I tried to create a new account myself using one of my throwaway e-mail addresses and had the same problem. And no, it’s not just being dumped into the spam folder. I haven’t changed any settings recently, so I don’t know what could possibly be the problem. Any ideas?

The site is phreakymonkey.com/blog