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IMAP performance in Outlook 2010

I upgraded to Outlook 2010 and I have the feeling that my IMAP account performance has become slower. Especially when switching folders, it takes quite a while for Outlook to become active again and shows “Not Responding” in the Title Bar.

Is there any way to speed up IMAP performance in Outlook 2010?

While IMAP performance is slower than for POP3, Exchange or Hotmail account in Outlook, long hangs or even crashes of Outlook should not happen. There is currently 1 hotfix available to improve Outlook’s resiliency when it comes to IMAP accounts which might improve your situation.

Aside from this hotfix, there are also some other things that you can do to improve IMAP performance in general (this also applies to previous versions of Outlook).

December 2010 Hotfix KB2459115

The December 2010 hotfix for Outlook 2010 contains several fixes including an IMAP related fix described as;

“Outlook 2010 stops responding when you configure an IMAP mode profile to connect to a large size mailbox.”

After further inquiry about this with Microsoft, this exact fix improves Outlook’s resiliency when it gets unexpected responses from the IMAP server. As Outlook checks for messages to update when switching folders and thus communicates with the IMAP server, applying this hotfix could also have a positive impact on the performance of that process. So, while this fix wasn’t focused on increasing Outlook’s IMAP performance, it does have this lucky side-effect.


When synchronizing an IMAP account, Outlook could momentarily hang
and display “Not Responding” in the title bar for a few seconds.

Note: This fix is also part of Service Pack 1 for Office 2010, so there is no need to apply this hotfix anymore.

Other issues

If the folder switching performance of the IMAP mailbox is still slow after applying this hotfix, it could be caused by one or more of the reasons below;

  • Virus scanner integration
    I’ve warned about this countless times before; having virus scanners integrate with Outlook is a bad idea and doesn’t add any additional level of protection. As it also slows down your send/receive performance and while IMAP isn’t already the fastest at that, you should really disable this if you still have it enabled.
  • Add-ins
    Have you tried already to run Outlook with all your add-ins disabled? If it runs quicker now, it could be that 1 or more add-ins simply don’t play nice with IMAP or are very resource intensive. You can then enable them 1-by-1 to (restart Outlook each time and check) to find the culprit.
  • Complex view
    Outlook indexes are optimized for views which are sorted by Date. If you are using a custom view with a different or additional sorting or grouping method or have filters applied, try if resetting your back to the default view increases performance.
  • Account configuration corruption
    A simple but in some cases very effective method is to remove the IMAP account, restart Outlook and then add the IMAP account again. As all the data of the IMAP account is located on the server, no data will be lost and Outlook will automatically begin re-caching the data from the server. Recreating the mail profile entirely could help too.
  • More requires more
    Due to the synching nature and method of IMAP, the send/receive process of an IMAP account has more to process than with any other account types. Folders with more items in them will also take longer to process. Having a faster system (faster hard disk or faster CPU) really benefits Outlook’s IMAP performance. If that is not directly an option, use sub folders and keep the folders that you access the most as small as possible (50 items or less would already be great).


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