said by ArrayList:most residential ip blocks are blacklisted from even exchanging mail with mail servers.
That is far from true. The only residential IP address blocks in lists are those preemptively blocked because the IP address block owner requested the listing, or they were reactively blocked for hitting spamtraps. The rest are not blocked.
I'm on business class right now. The IP address that I have now, I also had on residential. Port 25 has never been blocked for me to non-comcast email servers. Maybe I slipped through the cracks or something, but it is what it is.
When SBC announced port 25 blocking in October, 2002 (I still have that email announcement), it took them until March, 2003, to block my account profile.
The Comcast announcement seems to be fairly recent; give them a little time.