title: Outlook thrashes /mapi/emsmdb on non-domain-joined laptop
body: <p>We have a BYOD laptop with Office 2013 on Windows 10, fully patched, not domain joined, connecting to Exchange 2016 on-premises.  We noticed that when Outlook is running on this particular laptop, there are thousands of password failures going to a MAPI URL with the local logon account credential (computername\user) – this is from inspecting the NTLM handshake.</p>
  
  <p>POST /mapi/emsmdb/ MailboxId=@ &amp;CorrelationID=;&amp;cafeReqId=; 443 - IP Microsoft+Office/15.0+(Windows+NT+10.0;+Microsoft+Outlook+15.0.5059;+Pro) – host 401 1 2148074254 31</p>
  
  <p>Has anyone seen this behavior before?</p>