Russell from Port25 posted a comment on my earlier post about changes at Comcast.
Our (Port25) understanding is that Comcast is rate limiting such that they’re only accepting 6 recipients per second per sending IP.
This matches what I’ve been hearing from other bits of the industry over the last few days. I am recommending clients close the connection between each set of 6 email addresses.
Earlier this week a question came up on a mailing list. The questioner recently started seeing an increase in rejections to @aol.com addresses. These rejections said
Read MoreMatt has posted a bit more about the SenderScore Blacklist, following up on my post about the changes at Comcast. George Bilbrey, VP and General Manager, for Return Path followed up with him to explain a bit more about the blacklist. George says:
Read MoreI can usually tell when one of the ISPs makes some change to their incoming spam filtering just by my call volume. The past few weeks the ISP in most of my calls has been Comcast. And, what do you know, they have made changes to how they are filtering email.
According to their bounce message, Comcast is using ReturnPath’s proprietary SenderScore product to filter mail. Reports on thresholds vary, but IPs with SenderScores of 70 and below have been blocked with messages similar to: