An apparently common issue with Outlook for Mac 2011 is crazily high CPU usage, enough to spin up the fans on a desktop machine or drain the battery on a laptop, when Outlook really shouldn’t be doing anything.

If you do some Googling, you’ll find a lot of people complaining and almost as many recommended solutions. Updating to a version after 14.2 is a typical suggestion, as is deleting and rebuilding your mail accounts (ugh, no thanks).

Keeping Outlook up to date isn’t a bad idea, but the problem still persisted with the latest version as of today (14.4.3).

In my case, the high CPU usage had something to do with my Gmail IMAP account, which is accessed from Outlook alongside my Exchange mailbox. Disabling the Gmail account stopped the stupid CPU usage, but that’s not really a solution.

What did work was using the Progress window to see what Outlook was up to whenever the CPU pegged. As it turned out, there was a particular IMAP folder — the ‘Starred’ folder, used by both Gmail and Outlook for starred and flagged messages, respectively — which was being constantly refreshed by Outlook. It would upload all the messages in the folder to Gmail, then quiesce for a second, then do it over again. Over and over.

Outlook’s IMAP implementation is just generally bad, and this seems to happen occasionally without warning. But the Outlook engineers seem to have anticipated it, because if you right-click on an IMAP folder, there’s a helpful option called “Repair Folder”. If you use it on the offending folder, it will replace the contents of the local IMAP store with the server’s version, and break the infinite-refresh cycle.

So, long story short; if you have high-CPU issues with Outlook Mac, try the following:

  1. Update Outlook using the built-in update functionality. See if that fixes the issue.
  2. Use the Progress window to see what Outlook is doing at times when the CPU usage is high. Is it refreshing an IMAP folder?
  3. If so, use the Repair Folder option on that IMAP folder, but be aware that any local changes you’ve made will be lost.

And, of course, lobby your friendly local IT department to use something that sucks less than Exchange.