Hi,

This problem is too difficult for me, but I'm sure that someone with the
right knowledge will be able to diagnose it.

I have a dedicated server hosted by 1and1 running Plesk 7.5.2 on top of
Linux 2.6.9-041221.

For some unknown reason, when I came into work this morning, no-one
could log into the server using POP3. I checked using telnet and got the
following:

....
+OK Password required.
pass password
Connection to host lost.

At this point I knew that it wasn't something too obvious (as incorrect
passwords etc would give an error).

I logged in to the server to reboot it, but that achieved nothing. I had
to find the mail directory to back it up, which was at:

/var/qmail/mailnames/domain.com

I backed up all the mail and then tried to find docs on qmail to see how
to solve the problem. I gave it half and hour but couldn't find anything.

By this point I had some bounced test messages saying:

SMTP error from remote mailer after RCPT TO::
host domain.com [217.*.*.*]: 553 sorry, that domain isn't in my list of
allowed rcpthosts (#5.7.1)

I just cut my losses, deleted the entire domain in PLESK and rebuilt it
from scratch. It is now working fine and I am recovering the backup mail
now.

Does anyone know what the problem was and/or how to fix it if it happens
again?

Thanks,

John