By default the Server Timeouts setting in Outlook is low (~1 minute). When the Server Timeouts value is too low, Outlook can behave erratically (sending duplicate messages, not receiving new mail, etc). This can be the result of a larger mail box, or an extensive list of files and folders to synch with.
To increase the value of the Outlook Server Timeouts, follow these directions:
At this point, it is recommend to restart your computer to push through the settings.