On Small Business Server 2008 we have see that if you install RU3 you may start getting repeatedly prompted for log in credentials when opening outlook.
I believe that is because of some additional NTLM security that is put in place which I believe is included with RU3 based on this blurb in the update documentation
“After you install this update, the authentication mode that is set for the Web site at http://companyweb changes from the NTLM authentication to the Kerberos authentication. The reason this change occurs is because we recommend that you use the Kerberos authentication instead of the NTLM authentication.”
The solution I found so far was
- Remove RU3 for now.
- re-apply the Windows Authentication on the EWS, OAB, and Autodiscover virtual directories
- restart the server
Note: It may be necessary to add the root exchange URL to the “intranet sites” for on the clients
Tools -> Internet options -> security tab -> Local Intranet -> Sites -> advanced -> add -> https://remote.domain.com