OK, hear me out, I wouldn't believe this myself If I didn't had the evidence:

Somehow Windows Server, specifically svchost.exe decided to change the System Time 745 hours in the future, and I believe (not sure) that this was the root cause for my first MAPI Problems yesterday (Message in German):

*******************************************

Die Systemzeit wurde von ‎2022‎-‎01‎-‎31T14:31:24.191880300Z in ‎2022‎-‎03‎-‎03T15:31:23.661228700Z geändert.
Änderungsgrund: An application or system component changed the time.
Prozess: '\Device\HarddiskVolume3\Windows\System32\svchost.exe' (PID 3152).

*******************************************

and \Device\HarddiskVolume3 is my System Drive:

DevicePath               DriveLetter
----------               -----------
\Device\HarddiskVolume3  C:        
\Device\HarddiskVolume6  D:        
\Device\HarddiskVolume8  E:        
\Device\HarddiskVolume10 F:        

In conclusion, the 745 hours time offset, caused from svchost.exe seems to be the root cause of this huge MAPI trouble.

Would be nice if someone from SmarterTools could confirm this.

To be honest, I have no clue how and why Windows Server had to change the time 745 hours into the future.

I've now set different time servers in Windows, because I'm not sure if it was the default "time.windows.com" which caused this:

w32tm /config /update /manualpeerlist:"pool.ntp.org time.windows.com time.apple.com time.cloudflare.com"
w32tm /resync
w32tm /query /peers

Regards,

Josip.

Thanks for this breakdown Josip, the time change issues would definitely cause your sync to get out of sorts, and likely explains the problems you were having there. Once the time is corrected please give the resync user protocols option once more and let us know if you continue to have sync trouble with this client. As to the root cause, this time change behavior is something I've seen in one other environment where the time was changed erroneously via NTP updates, and so I've typically recommended to my users that they leverage manual time settings since time changes can be extremely detrimental to sync and mail servers in general. 

On the memory usage, please note that MAPI is a heavy resource user, and is designed to use the memory available to us to provide the best and fastest sync and overall experience for those users. With that being said, we would be happy to take a look for you and help confirm whether the resource usage you're seeing is reasonable or not. Please feel free to submit a review ticket with us and we'll help get to the bottom of it for you.