[BlueOnyx:09562] certain email doesn't arrive for a particular domain

[Adam Lepp]

I have a 5106R using MailScanner and SpamAssassin from Compass Networks.
Usually I can figure out any problems but this one is mysterious.

On one of my sites, emails sent via certain SMTP servers do not arrive.
They don't appear in MailWatch -- they're just sent and never arrive. One of
the SMTP's is the one from my ISP here in Ohio. The other is the one used at
my client's office -- so they're unable to send mail to each other via
Outlook! Messages sent from anywhere else -- including tests I've run from
AOL, webmail, etc. arrive quickly, as expected.

This site has several aliases, and mail (from all SMTPs) arrives in all
cases.

It isn't a blacklisting from the ISPs -- other domains on the server receive
email just fine, as do this site's aliases.
I have tried changing the virtual site name to one of the aliases, then
changing it back.  In all cases, email from AOL, webmail, etc., arrives
quickly but mail sent from my own ISP's SMTP never seems to reach
MailScanner.  Other ISP's SMTP servers work, and the site is tested with
WebSitePulse twice per hour with no failures since a (minor) incident last
week.

This problem appears to have started earlier this week. I did have to
restart the server on 2-3-12, when no users' mail went into their boxes.
There were extensive YUM updates may have had something to do with it.
After the restart everything was fine.  But then this unusual problem
appeared.

Would appreciate advice and potential fixes from my fellow BX community
members.

Adam