One more piece to the puzzle...
I just realized there is another possibly-relevant piece to this puzzle.
There is a single domain on this server for which I host a mailman mailing list. When I first moved that site and its list to my server a couple of years ago it was receiving a huge load of junk mail every hour of evey day. Worse yet the inbound email address most of the spam was being sent to was the same one the mailman list had long been hooked to.
So, when I installed mailman, I configured it to only accept mail from known list members and configured things so the server would bounce all mail that wasn't accepted by mailman back to the sender. Later I realized that this so-called junk mail "back-scatter" was an issue that caused some Black lists to rate the server poorly. So, I changed that bounce solution to accept all such mail and deliver it to >null instead.
As far as I know, it's still operating that way on that mailman domain. That approach shouldn't cause a black-list problem, should it?
Last edited by websissy; 28th October 2009 at 20:16.