I am having a terrible time since the last 10 days or so to get emails out to our friends using our FIOS internet at home, 1and1 as email provider and especially sending to Comcast (and others).
Warning emails come back with messages like this:
Received: from xxxxxxx (pool-96-227-235-109.phlapa.fios.verizon.net [96.227.235.xxx])
by mrelay.perfora.net (node=mrus4) with ESMTP (Nemesis).
What I found is that the above IP address from verizon.net (96.227.235.xxx) is listed on the "Return Path Reputation Network Blacklist." I found this through https://www.senderscore.org/blacklistlookup/.
Does anyone have a similar problem and possibly knows how this can be resolved?