I inherited administrative duties over an email server - postfix, dovecot, spamassassin, clamav, all running on Ubuntu Server. Everything "works" as far as I and other users can tell (except for one unfortunate soul). There is a backup email server that queues mail and sends it to the primary when it comes online, which has been successfully tested very recently. MX records are all in order and confirmed with third party DNS tests.
But here comes the headscratcher... one employee claims they are not receiving some important emails, but otherwise things work. And not just from anybody, from third-party auditors - who are usually very prompt and professional about their communications. This 'unreceived' mail comes from 2 company domains, and one guy uses yahoo mail. The user who has complained has provided me timeframes that the emails were claimed to have been sent in. Having checked through /var/log/mail.log's (and mail.err's) I see no mention of these email addresses. But I do see all of the other emails received in there. So from my end, it looks like everything is fine and we just have not received those messages. But this is a trustworthy, professional employee who swears up and down that they were sent but never received. I've even done dumb things like send 20 emails from my gmail to my work email to make sure they all get received, and without fail, I have yet to see one go undelivered.
Also - I get notice of all spam emails, bounces, and other oddities as the IT guy, and they don't show up in there either...
Anyways, dear gurus of /r/linuxadmin, I am running out of ideas as to what to check and what may be causing this. Is there anything that I could be missing here?? I am inclined to believe the user but I just cannot find any records correlating with the issue...
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