We've had a problem for about two weeks now.  All our Mac desktops running Office for Mac 2011 asks for a user name and password all day in Outlook.

One Mac is on Mavericks, the others are running version before Mavericks.  MacOutlook/14.4.3.140616+(Intel+Mac+OS+X+10.9.4.  From Mavaricks Mac.

The problem started all of a sudden.  No one patched their Mac desktop at the time and the Exchange server wasn't patched either.

The problem could have been certificate naming issues where the server name doesn't match the name on the cert.  I made an allowance for this with Powershell.  Autodiscover asks to redirect to the correct server.  This happened only after recreating the ESW virtual directory.

Also tried:

- Deleted and recreated the EWS virtual folder with Powershell, but the problem still exist.

- Create a new user in Mac and created a new Outlook account.

- Delete and recreated Outlook account on an existing user account.

- Fully patched Office for Mac 2011

- Fully patched Mac OS X.

- Started Outlook with Options button.

- Tried domainusername format for logon

- Added server name in the certificate to the Network settings> Proxy servers in Mac.

- Patched Exchange 2010 completely and restarted it.

None of the above has worked.

In the Exchange 2010 server log, I found many of the POST lines show no user name for Mac IP addresses.  Here's an example:

2014-08-21 11:55:05 <Internal Server IP> POST /EWS/Exchange.asmx - 443 - 192.168.1.62 MacOutlook/14.4.3.140616+(Intel+Mac+OS+X+10.9.4) 401 1 2148074252 0

Other POST line show the user name:

2014-08-21 12:00:23 <Internal Server IP> POST /ews/exchange.asmx - 443 <DomainUsername> 192.168.1.62 MacOutlook/14.4.3.140616+(Intel+Mac+OS+X+10.9.4) 200 0 0 156

There are specific logon errors in Exchange event viewer regarding empty user names.  Event ID: 4625.

Also seeing a few 4776 cmputer attempted to validate the credentials for the account.  These have the Mac users' logon account.

Error code: