Originally, all of our users were on a single domain (ie. domain1.com) . After merging with a 2nd company, it was decided that we would use the 2nd domain (ie. domain2.com) as the primary company domain.
To transition, all users in domain1.com had mailboxes created on the domain2.com Exchange server, and we put forwarding in place back to domain1.com so users would be able to receive emails on both email addresses: user@domain1.com and user@domain2.com.
PROBLEM: As part of the transition, it was decided that BY DEFAULT our users should send email as user@domain2.com. So, on the domain1.com Exchange server, each user has 'user@domain2.com' as the primary email address. Immediately after this, multiple users were having issues logging into their Outlook clients, several reports of users being locked out of their PC's (which use domain1.com credentials) and other services.
The theorie we have -- 1) changing the default address causes the Outlook client to authenticate (autodiscover) the domain2.com Exchange server -- the authentication fails, and somehow the user gets sent back to the domain1.com Exchange server (maybe as fail back?) and in that case the authentication fails because the user@domain2.com user does not exist on the domain controller.
How can we find out WHY the accounts are getting locked out after a change in Exchange?
