We've had mac users who at some point in time get a message that prevents them
from being able to use pop to get their mail. Once that email message is deleted then they can suddenly use their email
account again.

Any ideas?

(Its only been the mac users who have had this problem).

I didn't see anything helpful in the logs.. just that they tried to log into
pop, and there was a big number in TOP, and retries were several times I
think... actually they were actually all quite random numbers...

Note - the last time this happened it was a local user sent global email so
other users mac and xp still received the message fine, and it wasn't a message
from some spammer / virus maker etc. But it prevented one mac guy from being
able to use pop to get his email. He had to go into webmail - and once he
deleted that message he could d/l his email via pop again.