I have since the introduction of Office 365 in our organization in 2014 tried to get an Outlook bug fixed. The bug is present in the 2013 and 2016 versions of the software; both for 32 and 64 bit. At the moment, I am running the latest and greatest: Office 2016 64 bit, Version 1710, Build 8625.2127. I have observed the bug since using Office 2013 32 bit in 2014. A lot of tickets and emails back and forth, but the bug is still there. Hence, I hope someone from Microsoft might be reading this forum and might be able to get this bug squashed once and for all.
The bug hits rarely and can be observed by some email messages not being shown in certain mail folders. At the moment I can see 14 top level messages in my Inbox on my Outlook 2016 fro Windows client. Using OWA, I see 2 additional messages; Outlook looses track of some messages in my Inbox. Once this happens, Outlook looses track of that message "for forever" and it does not reappear. The oldest of these invisible emails is from early August(!).
Hence, Outlook does not seem to perform a full check of a mail folder at standard intervals. Something which requires the quality of the mail folder checker methods to be extremely high...
The only known hack to make them re-appear is to delete the local .ost cache, something which is unacceptable for an enterprise mail system.
You do only observe the bug if you have multiple clients connected to the same mail account. (I have never had the same mail message go invisible on me on two clients at the same time.) If you only connect to your email account using one client, you will most likely never be made aware of the bug; you will only think you have deleted the email that you cannot find.
I have only seen the bug on Outlook for Windows and Mac. Never in OWA. Never in the iOS Mail app. Never in the iOS Outlook app.
I am not sure whether the bug is limited to my Inbox folder, but that is the folder I use the most.
Any answer will be greatly appreciated. Thanks in advance.