The Business of Software - UPDATE: Getting filtered as BULK/SPAM/JUNK on yahoo/gmail/hotmai
"The problem was that all emails from my web application were going to the spam/bulk/junk folders on each respective service. These aren't spam emails, these are simply "confirm your email address" emails.
It's been a long process, but with the help of lots of useful tips from other developers I've been able to resolve most of the issues."
http://discuss.joelonsoftware.com/default.asp?biz.5.549659.3