I waited 5 hours to see if the problem resolved itself, but at the moment almost everything is still blocked.

I'm thinking of going back to the previous version ...

Try to reboot the server.

We did install a customer build and CPU went from less than 10% to 90+.

I restarted the smartermail service but it didnt really help.  

After a full server restart it went back to normal.

Not sure if it will help you but it did for us so maybe worth trying.

Heimir, server reboot... Let's see if works

For now it seems to be going better...

But I still notice an increase in CPU usage: normally on my server the SM service has always been between 0 and 1% (in rare cases a bit more).

Now, even after rebooting, it's fluctuating between 5% and 20% ...

Gabriele, keep us updated if you still have problems during the weekend ;)

OK, I understand what happens ...

In my tests (I am using my production server with over 600 active POP3 and IMAP mail accounts) I have removed and resynchronized a large MAPI account with my Outlook 2016 and during MAPI synchronization the CPU used by the SmarterMail process goes from 5% to 9% (with 20% peaks). Once the synchrony is over, it returns to steadily drop below 1%.

Calculating that this is the one and only account that uses MAPI (still testing) and that I have a 3.3GHz Xeon E-2136 CPU, it seems to me that SM's CPU consumption is a bit exaggerated ...

What will happen when I have 2-300 users configured in MAPI?

I'm going to investigate this behavior a bit deeper, @Gabriele, I've got a couple questions that can help me reproduce the behavior.
How large is the account?
Is it primarily a couple folders with a lot of data, or a lot of folders with data?
How many calendar appointments, contacts, etc?
Is this the first time the account was synced?
During this period of high CPU was other experiences impacted? )Were login times slow, loading accounts slow, etc.)

Thanks!

@Gabriele I have generated a support ticket from this community post (at the request of development) and have reached out to get the ball rolling on this. Please follow up with us with those details noted in the ticket and we'll get this going in the right direction as soon as possible. Thank you in advance. 

Hi Matt and Kyle!

The account is the same that is monitored in ticket 376-271806A5-0B53 fo another issue..

It is indeed a big account (about 20GB of data)

Clarifications:

1 - rebooting the server the CPU is no longer 100% busy

2 - I noticed that there is (in my opinion) somewhat high CPU usage (5 to 10% with peaks up to 20%) only while syncing the account for the first time (I can replicate this by deleting the account in Outlook and then recreating it).

3 - Once the first account synchronization is complete, the CPU usage returns below 1%

We are experiencing the same high CPU usage issue since the Build 7642 update I performed earlier this week. Yesterday I even had to restart the server because the consumption of the processors by smartermail service skyrocketed to 100% in the middle of the afternoon. After restarting the server, Smartermail's service went back to very high consumption (around 45%), so at the end of the evening, since the processors didn't want to go back down, I decided to restart it again.

During the night, everything calmed down, but today the Smartermail service has again started consuming around 35% to 40% of the power without ever going down, while before the update the average consumption during peak periods was 16 % with build 7619. I'll probably restart again at the end of the evening if things don't calm down.

Am I opening a ticket or is it a known issue that you are fixing?