This is kind of a shot in the dark, but it's possible that it uses some sort of settings auto detection and gets the mail server wrong. Was the account added, or did it get aborted before you got that far? If the account is actually there, try going to Settings -> Mail, Contacts, Calendar -> [your exchange account] -> Account Info. There you've got separate fields for Server and Domain - you may have to specify both for accounts not on domainA.
HTH.
Sverre