Double check your Outlook VSE exclusions; Plan antivirus scanning for Outlook 2013
Old KB, it may be worth reviewing the MS link to see if it applies to your environment:
"Cause: While this appears to be caused by the VSE Email Scanner, examining a Windows Performance Recorder Trace of the node reveals excessive wait time being consumed by Microsoft MSO.DLL.
Solution: This issue is not caused by VSE 8.8. Microsoft has indicated that correcting the Autodiscover provisioning alleviates this problem. Autodiscover is the mechanism used by Outlook to find the appropriate Exchange server. If Autodiscover is incorrectly provisioned, it can cause Outlook functionality to be dramatically impacted."
Slow performance with Microsoft Outlook when the VirusScan Enterprise 8.8 Email Scanner is enabled Technical Articles ID: KB86832 Last Modified: 3/22/2016