From what little I understand about all this technical stuff, it looks like my pop mail to comcastbiz.net gets pushed off through the comcast servers at the address in red below.
That kinda implies that someone is phishing or otherwise pushing bad packets out of that address and someone else's spam filter took exception to it, to the point that my business email is now bouncing - which is not a good reason to pay ten times more for a Comcast business account than I do for my Yahoo pop mail account.
Time to step up, Comcast, and protect the interests of your clients.
Reporting-MTA: dns; omta02.potomac.co.businessclass.comcast.net [188.8.131.52]
Received-From-MTA: dns; [192.168.2.40] [184.108.40.206]
Arrival-Date: Tue, 08 Oct 2013 15:32:18 +0000
Final-recipient: rfc822; firstname.lastname@example.org
Status: 5.1.1Diagnostic-Code: smtp; 550 Rejected message because 220.127.116.11 is in a black list at bl.spamcop.net
Last-attempt-Date: Tue, 08 Oct 2013 15:32:19 +0000