We have a user that says they didn't receive a few emails from an outside address last week. I checked our spam filter which is a separate physical server from exchange and I can see the email passing through that as it was whitelisted. I verified the internal address and also confirmed that this remote user has been able to send to the internal user in the past.
On exchange I went into the message tracker and see those emails that never went through. Again made sure the internal address was correct.
I pulled up the users account and nothing showed up in deleted items, inbox, etc.. I did a search of the mailbox and it found an email from this user from a few months ago. I also looked at "recover deleted items" and nothing showed up.
Also checked auto archiving and it is setup for every 14 days, so that rules that out.
Not sure if there is a way to track the message any further with a tool on exchange or a way to dig any deeper to locate the emails.