I've been using Yahoo mail as a filter for a good 10 yrs.(?) but I have also been using Mail since it's first iteration and have not had many problems. I open both my Yahoo mail and .Mac mail in the Yahoo web site, delete all the junk then open Mail and it downloads what's left. I use Mail to respond, forward , etc., it's a convoluted process I know but it seems that for me the Yahoo filters are more robust, that may have changed over the years and Mail may now be as good but for me it doesn't seem worth the trouble. :-). I have Comcast cable/internet but have never used their mail system, for that matter I only used their predecessor's mail system for a very short time (less than 3 mo.) so I'm not familiar with any of the problems you mention specific to Comcast. I will say that my father-in-law used their system on his Mac (Mini running Tiger 10.4.x into Leopard 10.5.6) and did not seem to be having any problems, he handled the account set up and had he had any issues he would have come to me first since I'm the one that persuaded him to make the switch to Mac.