We were finish with setting up Exchange 2010, published OWA, ActiveSync Outlook Anywhere (KCD SSO) with co-existent with Exchange 2003 trough ISA. Everything worked good. Autodiscover externaly worked perfect.
When we tested mailbox internally we saw that Out-Of-Office did not work. I’ve checked Autodiscover from Outlook client and it searched Autodiscover from wrong SMTP address?
I found out that it was the UPN name that it used which caused autodiscover to fail (it is not the same as SMTP address in this case).
I found that update http://support.microsoft.com/kb/2412171 could cause this problem, and we uninstalled this update. No improvements.
I then installed KB 2475891 http://support.microsoft.com/kb/2475891 . Then the primary SMTP address was used. And Autodiscovery worked as it should.