I am going to repost the steps I took to fix this issue here.
What I failed to mention before is that there was an additional step I had previously taken. During this previous step I applied a fix and thought it had resolved my issue, but the CPU spiked again after a reboot... however it may be relevant to the overall picture.
This was the first step I took: (Reference: https://buymymonkey.wordpress.com/2019/10/27/osx-catalina-cpu-spike-checking-mail-after-upgrade/)
- Make a backup of Apple Mail messages if you store anything locally (like storing something On My Mac, downloading via POP3 etc).
- Go to System Preferences > Internet Accounts.
- Delete all Exchange accounts.
- Delete ~/Library/Mail and ~/Library/Containers/com.apple.mail folders (this will reset Apple Mail and its preferences).
- Restart the Mac and uncheck “Reopen windows when logging back in” to make sure Apple Mail won’t start after rebooting.
- Go to Internet Accounts, click on +, select Exchange, enter your name and email address.
- Click on Configure Manually and enter your password.
- Uncheck everything (like Contacts, Notes, Calendar etc) and leave only Mail checked. You will be able to add it later (see below).
- Start Apple Mail and go to Preferences > Accounts.
- Select your Exchange account and click on Server Settings tab.
- Uncheck “Automatically manage connection settings”.
- Make sure both Internal and External URLs are set to https://outlook.office365.com/EWS/Exchange.asmx.
- Close Preferences and restart Apple Mail.
- If you need Contacts and Calendars, go to System Preferences > Internet Accounts, select your Exchange account and enable the services you need to sync.
I applied the above fix and for a day all worked well until I rebooted my machine. After digging into the console again I noticed an kernal error that pointed me to the addressbook being corrupted.
That kernal error looked like this:
To fix the corrupted addressbook I applied the following steps: (Reference: https://appuals.com/fix-mac-running-slow-due-addressbooksourcesync/)
I first Quit Mail.
Back up your Contacts locally and then quit Address Book (Contacts).
- Launch the Contacts
- Click on File from the menu bar at the top of your screen.
- Click on Export.
- Select Contacts Archive.
- Choose the location where you would like to save the file.
- Set the name for the file, and click on Save.
Now, go to icloud.com and check if you have all of your contacts there.
Launch Activity Monitor and make sure AddressBookSourceSync is not running. If it is, double–click it and select Quit from the window. (** I did not see this process running)
Now go to your user’s library (~/Library/Application Support/Address Book/).
Delete everything within this folder (backup if you want, but it will all get regenerated)
Now, go into System Preferences and click on iCloud.
Navigate to Contacts and check off the box.
Now, recheck the box, and the sync will start. Give it about 5 min and youll notice that your contacts have regenerated and those files you had previously deleted have been regenerated.
Once the contact were back, I restarted mail and have had 0 issues for the past 4-5 days.
I hope this helps others.