Occasionally, some or all email messages in a particular folder may be duplicated in Microsoft Outlook for Mac 2011. For example, this issue may occur for the Inbox folder or the Sent Items folder. This issue seems to occur most frequently when there are lots of email messages in a particular folder.
This issue has been confirmed to occur on the Snow Leopard and Lion operating systems when McAfee Internet Security 18.104.22.168 is installed. However, it may also occur on other versions of these products.
When McAfee antivirus software is installed, the size of data files against which Outlook called the file system operation FSExchangeObjects may incorrectly change to 0 bytes after the system restarts.
When the data files that incorrectly undergo this change are critical files that store the sync state, Outlook may generate duplicate email messages. Depending on the files that are affected, this incorrect behavior may also cause other problems.
To work around this problem temporarily, exclude the Outlook for Mac 2011 database, its data records, and the Office temp folder from being scanned by the McAfee antivirus software. The specific directories to exclude are as follows:
/Users/<username>/Documents/Microsoft User Data/Office 2011 Identities
Microsoft has reported this problem to McAfee, and McAfee is investigating a solution.
The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of these products.
Outlook 2011, Outlook for Mac 2011, duplicated email