I've got a bit of an odd situation.
I've got a user who works for two different clients. Both Client A and Client B run their own sbs 2003 server running exchange.
User is member of domain for Client A and that exchange account works fine both on and offsite. However, exchange for client B works neither on nor offsite, refuses credentials.
Originally, the user was primarily at Client B location. He was connected to their domain and e-mail worked fine both on and offsite. We connected him to Exchange for Client A through RPC. Took a bit of fiddling, but then worked fine.
After a couple of years, the companies got rearranged. I reloaded the user's laptop. I added it to the domain for client A. E-mail works fine on and offsite.
However, no end of trouble connecting to exchange for Client B. Finally took laptop to location of Client B. got working locally. Took back to Client A location, would not work. Traced error to certificate. Bought new certificate and installed. The error went away, but now credentials fail. This happens on and offsite now.
I have tested and retested the credentials for owa. They work fine. I can use both user and domain\user to successfully login.
On the laptop though, I think I am forced to use domain\user as otherwise it assumes the domain for Client A.
This user also accesses both exchange accounts without issue.