What can I do when some of my yahoo mail from specific sites is not being delivered?

I have registered at some sites to receive information or newsletters. In one case, I have registered to participate in forums on the site but can't because the confirmation email from that site has not been delivered to my Yahoo! mail. I have added these sites to my address book and I have set up filters so that when those sites' names appear in the "from" section, they are directed to my inbox. I have contacted these sites for help. They say that I am registered, and have done what I should do, but the problem is with my mail service. I have a problem report in to Yahoo! mail. The automated response email suggested looking in Yahoo! Answers. What else can I do?