Over the last few weeks some of our users have complained that they are not recieving some external emails. This problem is very intermittent and is not limited to specific users or senders.
We have Small Business Server 2003 as our exchange server and a sonicwall email security box as our spam filter.
The mails in question have been addressed to several of our users, in all cases one or two users do not recieve the mail and the others do.
Message tracking shows the messages arriving (with all recipients correctly listed). However, message tracking does not show the message reaching all of the mailboxes. There are no errors listed in message tracking, and the senders have told me that they are not getting NDRs.
I have checked the junk box on our spam filter and the messages are not getting filtered out there, we have no additional mail filtering in place.
We have no clue why this could be happening and would really appreciate any advice.