This is going to be a long one so best grab yourself a tea or coffee before reading!
We have a single domain with 2 DCs - 2K3 AD, running Exchange 2K3 but in the process of migrating to Exchange 2K7 - Simple Exchange 2K7 install, nothing complicated. - Clients - XP SP3, couple of Windows 7 machines in testing for upgrading all XP machines.
The problem -
We have moved most (90%) of our users across and everything appears to be fine, they log on, launch Outlook which automatically reconfigured them to the new server and everything is happy.
Then we had a user log into a Windows 7 machine and setup their profile - unable to find the settings using Autodiscover - The usual error
Autodiscover to https://mailserver.domain/Autodiscover/Autodiscover.xml
Failed (0x80072f78) - Now doing major amounts of research always points to the 2 same things as the cause - Certificates and permissions on IIS - However this is not the case.
Upon further testing I have found the following - Any new account that is created on the domain can quite happily login to XP or Win7 and autodiscover works a treat.
Accounts that have been created by myself in the past 2 years all work on both XP and Win7. (Prior to this date I wasn't the Network Admin)
So far every old account (Over 2 years old) fails on the Win 7 machines, but works Win XP. I've used ADSIEdit and LDAP Browser to compare settings of working and non working accounts - Everything (Apart from GUID etc) are correct (Exchange details, legacy details, etc) in both working/non working accounts.
If I take a non working account, delete it, recreate it and reattach the mailbox then it happily works on both - This is a workaround, but not a solution, I'd rather not have to do this with all our users!
I've done a lot of research on this and found 1 other posting on the web where the same thing happened, they found a setting in the users AD account that they updated and it fixed the error (LegacyDN) but this fix doesn't work for us.
I'm 100% sure it's a setting somewhere in the users AD account that basically stops them from connecting to Autodiscover, but I'm at a loss as what.