Just process of elimination. Try multiple different email addresses to ensure it's not a problem with one specific address. Check your spam folder. If the email is flagged as spam then check these things:
I can attest to this requirement. Microsoft has made getting removed from their lists much easier recently, but 2 years ago it wasn't so easy. In fact, it was a nightmare. Even after getting the requirements in place, it still took me close to a month of daily emails to Microsoft to finally get removed from their blacklist.
Email is a touchy issue for many sites. And it gets even worse if you send out mass emails to your membership. Get enough of the membership reporting your emails as spam, and you find yourself back on the blacklist again. I constantly remind the membership that they can opt out of mass emails, and if I find anyone reporting them as spam, taking a chainsaw to their membership account will be the least of their worries.