I have heard from a couple people that Yahoo! Mail will not send messages to my new email address. Below is a screen capture demonstrating this (not that I doubted them):
My email address is indeed valid, and I have now sent and received hundreds of emails using it. Furthermore, the specifications for email addresses are very simple, and my email address follows them (obviously). Yahoo! clearly needs to hire someone who can read a Wikipedia page and write a simple regular expression validating email addresses. Actually, a quick Google search (natch) proves that this has already been done dozens of times.
Just yet another reason why I'm glad I finally switched away from Yahoo! Mail. Good riddance.