Worried about Exim, my mail is dissappearing?

[Lucas Barbuto <lucas@qk.com.au>]

Hi List,

I've been running Exim for a few months at a smallish office site,
recently I migrated the system to Courier-IMAP (with Maildir format
delivery by Exim).

A few weeks ago a user complained that they hadn't received some mail
from a friend that had tried to send them some messages.  I checked the
logs, didn't see any errors, didn't think much of it.  However, today
I've had two more users complain of similar problems, not receiving mail
from friends, and not being able to send mail to friends... and when I
thought about it, I'd noticed a couple of occasions when I hadn't
received an email that I thought I should have.  I also had a suspicion
that the volume of mail I was getting from this list had dropped.

So the problem seems to be that somewhere along the line, mail is
getting lost.  There are no messages bouncing and no errors in the Exim
logs.  It's like the mail just dissappears into the ether.  This only
happens for mail to and from remote sites, in house mail seems to be
working no problems.  It also only happens intermittently, for example,
I'll ask a question on firewall@lists.debian.org, I'll receive a copy of
my message and maybe one reply, but then I'll go and search the web
archives and find two or three replies.  The problem also doesn't seem
to discriminate between senders and recipients, it can happen to anyone
either trying to send or receive mail.

This is weird and I don't know where to start looking, I've been tailing
the Exim logs all day and I haven't noticed anything unusual.  Has
anybody seen this kind of problem before?  Can anyone offer any ideas on
what's happening?

I've also read the Exim FAQ and found nothing helpful.

Thanks in advance,

Lucas