sendmail rejecting good mail?

[Fred Martin_1]

I just updated sendmail to v.11.1 and installed the security patch after that.

Since then sendmail rejects a lot of email, claiming the sender's domain must resolve.

As near as I can tell though, the sender's domain -does- resolve and I don't see why sendmail is rejecting.

For example, in one log record,

The sender is: User@msad51.org
The relay is: g4mailserver.ghs.sad51.k12.me.us [207.166.234.135]

Error is: reject=451 4.1.8 Sender domain must resolve

An nslookup (from the command prompt of the unix machine running sendmail) for msad51.org and the relay host show they both resolve to the address shown.

Earlier today I watched the logs and saw a user try to send an email to my server four times, the first three were rejected as above, and the fourth was accepted on the same exact address.

What could cause such a thing?

[Fred Martin_1]

Attached are the log entries for an email attempt which failed, followed by a success a few minutes later....

[Steven E. Protter]

I would look to problems with the DNS server.

Do they work right? Is it the same box as the sendmail box. Thats how it is with my basement based NSP.

If you connect to an outside public Internet DNS server, it may be going on and offline, or it may have problems with its configuration or root server setup(Those haven't changed since 1997).

I'd go through /etc/resolv.conf, reduce it to one nameserver and test them all with dig commands, repeat the domains giving you trouble.

If the answers are not consistent, you have a problem with the Name Servers.

SEP