View Single Post
Old 29 Jan 2017, 05:32 AM   #13
jhollington
Essential Contributor
 
Join Date: Apr 2008
Posts: 371
Something else that just occurred to me.... You may want to ask Freehostia is they use "greylisting" as part of their anti-spam procedures.

Broken greylisting could certainly cause this problem. It would be easy for somebody at Comcast who knows what they're doing to see this, but I'm left with the impression that Comcast isn't letting you talk to anybody who actually has that level of skill

In a nutshell, what greylisting does is to initially reject any messages that come in from a previously-unknown server using a temporary SMTP failure code (e.g. a "4xx" code as discussed above). The idea here is that most spammers won't try a second time after an initial failure, whereas most legitimate mail servers will. The receiving server (which would be Freehostia's in this case) is supposed to keep track of each failed "greylisted" attempt so that the message gets let through on the second pass, but of course if this is broken it's entirely possible it could keep failing the message until Comcast just gives up and rejects it outright.

Without getting into too much technical detail, if it's not properly implemented, it's pretty easy for this to break with certain major service providers like Comcast due to the use of multiple servers to send messages. I gave up greylisting on my own servers and many of those I support for clients years ago for this very reason, not to mention that it also can delay delivery of inbound messages, which many clients are never particularly thrilled about.
jhollington is offline   Reply With Quote