I am also being blocked (not by Comcast) but by UCEPROTECTL2 blacklist

I would, but the options available do not include "I cannot send email to others sites."  I am definitely able to send to Comcast.com/.net addresses without any problem.  I should point out that after reaching out to the specific site that was not accepting my email (a large university) the problem is currently 'solved.'  The UCEPROTECT site still claims a few thousand comcast IP addresses as being blocked (I could include the list here, but it's several hundred lines, so I will only do so if asked.)  UCEPROTECT may be doing a useful 'service' by noting 'communities' of bad actors, but the finger is really pointing to Comcast for not regulating their customers mis-behaviour.

Although I do believe UCEPROTECT has fairly low standards as to what constitutes 'abuse' and grouping multiples in specific  ARIN block subnets means for any reasonable large subnet, such is the 50.128.0.0/9 I am in, it encompasses more then 8 million IP address.  They seem to be triggering their 'abuse' status as less than 0.1% of the total users in that block alone.

I know this SPAM problem is difficult to resolve and I believe Comcast is doing a pretty good job of getting it mostly right.  I ssee the periodic notices intrusions blocked and SPAM they've preventing hitting my servers and am thankful.  But, according to UCEPROTECT, a self-appointed 'protector' of our email, it's not enough.  Comcast should reach out to UCEPROTECT ensure this 0.1% of abuse doesn't cause the other 99.9% (such as me) to have problems.

@aerodesic We appreciate the information, but I would also recommend to reach out to UCEPROTECT to see if they will unblock from their end since they are the ones that did it. My team is here if you should need any further assistance. 

@Comcast_Janelle​ I did reach out the quality assurance (postmaster) site and files a request, per a tier2 conversation.  But FYI, I did not do this initially because the postmaster link in my rejected email from comcast, showed two black list codes: BL000100 and BL000200.  The postmaster site requested it be used *only* for code BL0000000 rejection notices.  The tier2 person who send me to the site suggested the information display on the web page was 'old' :-).  Anyway, it was posted and we'll see if it does the trick.

Followup: checking my postfix logs, I see there have been no rejected DNSBL messages since about 5am this morning (it is not about 5pm.)  Longest stretch so far!  My postfix queues are empty and things again, purring along peacefully.  I will reach out again if things go south, but so far it looks like y'all did what needed to be done.  Thanks.