Static IP and Small Business Server

I have Small Business Server 2008 with Exchange 2007. I send and receive email from my server for my own domain. I have had the current configuration for three years and have had no problems until a few months ago. Sending and receiving email went from a few seconds to hours or days or no delivery at all. I called support for weeks and got the same story that Comcast has made no changes to anything related to email and there are no blocks or filters for ports. After a month a support person admitted that a new security feature had been implemented to reduce SPAM. A tier 2 person said I should have requested a PTR record. That’s hard to do when I don’t know I need one. The PTR record was created but that didn’t resolve the problem. I checked blacklists and found my domain was on a few for “missing PTR record”. I got removed from the black lists but I still have the problem. Another business I know has the same configuration and started having the same problem. They didn’t know about the PTR record either. They could no longer use Exchange on their server and started running email through their domain host. That corrected the problem except for mail going to any address at Yahoo. Mail to Yahoo was delayed just like when they were on Comcast. Yahoo had designated their domain as a bulk mailer even though they never do bulk mail. Yahoo support corrected the problem. The bottom line is, how do I get email working on my server again?