One difficulty with running a web site that sends emails: it’s very easy for your generated emails to get caught in spam filters. And the big email providers each have their own techniques for determining what is spam. This can mean that certain providers routinely don’t deliver your emails. For example, Tabblo and Hotmail just don’t get along that well.
I just saw this on TVGuide.com:
Sounds like TVGuide got fed up with trying to appease certain spam filters.