Alright... I have spent HOURS with xfinity about this issue and have talked with 3 levels of security and this issue is still not fixed. I have recently been made aware from admissions at a school I am trying to get in to that their emails to me are getting blocked by Comcast, and I am not receiving ANYTHING. I have tried anything and everything google has told me (checked spam, added them to my contacts, unchecked spam filter, etc). Nothing is working! They are getting "Comcast block for spam. Please see http://postmaster.comcast.net/
If @ComcastAntiSpam or another employee doesn't reply to your message here, Comcast Security Assurance should be able to help. You can reach them at 1-888-565-4329 (from https://internetsecurity.xfinity.com/help/report-abuse/). Note that this is NOT one of the general customer service numbers. The first-line reps there are sometimes not very helpful, so you may need to be persistent and keep at them until you get a satisfactory answer.
@stpbade3 Please provide the IP addresses involved if you have them, otherwise, the domain should also work.