I have a problem with internal mail flow. On one shared mailbox I have this issue, that when email is sent to it, some users don't get it. It's Microsoft Exchange Server 2016.
I did use Test-Mailflow and was logged in over OWA, to confirm this case.
What I have seen is that I have successful Test-Mailflow Result, and mail do arrive at it's destination, but disappear after a second.
Why is this happening I was not able to understand, but what I did found out is when I restart Microsoft Exchange Information Store service, it starts working fine.
But after a day or so, this problem happens again.
Does anyone had similar problem so far?
Update #1
Here is MessageTrackingLog.
You can see it here log for one particular internal mail which is problematic.
*note
One user which was not reached, is no longer exists.