Outlook 2010 is mixing up header IMAP accounts

Several messages in my IMAP account in Outlook have message headers (such as subject and From address) which do not apply to the message body.

The message body appears to be from previous emails, show garbled or can't be downloaded at all. Attachments seem to be affected as well.

Why is this happening and how can I fix these messages?

This issue is in part caused by a bug in Outlook 2010. A fix for this bug has been made available in Hotfix KB2597137 (released: February 28, 2012).

An email message body contains text that is added from previously opened email messages when you access a mailbox by using an IMAP4 client in Outlook 2010

More details and alternative solutions

More details about this bug are published in KB2597991.

Here it is explained that “the issue is caused by network communication problems during email message synchronization” and how the hotfix solves it by “clearing the internal memory during email message body conversion when network communication problems occur.”

While these communication problems could occur server-side, they are often also caused by client-side issues. Common causes are;

  • Having a virus scanner installed which integrates itself with Outlook.
    This something that is heavily recommended against as they are a common source of various issues and do not add an additional level of security anyway. For more details see; Disable virus scanner integration?
  • Having a firewall installed with a packet inspector activated.
    While this might not directly be a bad thing, they are a known source of issues as well. Disable it and see if the issue goes away. If so, reconfiguring your firewall/packet inspector or updating it to a later version might solve your issue as well. Otherwise, contact the vendor of your firewall/packet inspector solution to further troubleshoot your issue.

Fixing the broken messages

The proposed solutions in the KB article to fix the affected messages are a bit drastic though; “delete and then re-add the user profile, or create a new profile for the current user.”

Similar effective but less drastic solutions to restore the affected messages (after applying the Hotfix) would be;

  • Log on to the web based mail client for your account (or use another IMAP client) and move the affected messages to another folder. Force a sync of your IMAP account in Outlook by pressing the Send/Receive button or by pressing F9. Afterwards, you can move the messages back to their original folder and resync Outlook again.
  • Rename the pst-file of your IMAP account to .old when Outlook is closed. When you now restart Outlook, the IMAP account will rebuild the entire cache. To determine the location of the pst-file of your IMAP account use;
    File-> Account Settings-> Account Settings…-> tab E-mail-> select your IMAP account-> the delivery location is displayed at the bottom of the dialog.
  • Remove your IMAP account and then re-add it again.

Requesting the Hotfix

To obtain the Hotfix, you’ll need to request it via the link at the top of the KB article or use this direct link to the Hotfix request page instead.

The fix should work directly after installing it; no additional configuring or resetting is required to make it work but you may need to restart your computer to complete the update process.

Hotfix Download Available
Hotfix articles have a download request banner at the top.

Unlike regular updates (which are being offered automatically via Windows Update), Hotfixes are basically pre-releases of updates that haven’t gone through all possible testing yet and are only meant to be installed to solve issues mentioned in the article. If you are not heavily affected by this issue, it is recommended to wait for the next public update or Service Pack which will also contain this fix.
For more info about Hotfixes see; What are Hotfixes?