If you search the threads I think there is something about this issue, on initial update all email boxes need to be reindexed which results in high cpu and ram usage until complete.  Hope this helps.

Check you JSON file sizes... This was the cause for us... Apparently, when JSON files are large then 10Mb you start filling up RAM, and you start getting lots of hard Memory Page Faults we well, as Windows wants to load the entire file contents into the memory. Since some of the JSON files are read a lot scanning memory adds to the CPU load.

Hi Faith, 

I see you upgraded from Build 8601 to Build 8629. This shouldn't have caused any user conversions, reindexes or the like, so I'm afraid the high CPU/RAM is unexplained at this point. Is this problem still occurring? Or has it since resolved? 

If you're still seeing spikes, please open a support ticket so we can help to assist you. If the spikes have stopped and you have a backup of your SmarterMail installation from before your upgrade, you can still start a ticket as well. If you can provide the backup, we can stage it locally and see if this behavior can be reproduced. 

Kind regards,