Thank you for taking the time to read this. I've been banging my head on why this must be or I've got something wrong with my hybrid configuration. I have a Full Hybrid environment setup between on-prem Ex2013 and O365 and it works great except the autodiscover part.
user@DOMAIN.com is the default SMTP address of this local domain user whose RemoteRoutingAddress is user@DOMAIN.mail.onmicrosoft.com. Autodiscover is pointed to on-prem Ex2013 because that's what you're supposed to do until all mailboxes are off of the on-prem Ex2013. Outlook finds the autodiscover.xml correctly but the RedirectAddr value that Ex2013 returns is the RemoteRoutingAddress value instead of the Default SMTP Address value for this user so unless the Office 365 UPN for this mailbox matches the RemoteRoutingAddress, Outlook fails to complete setup. How can I make Ex2013 return the Default SMTP address as the RedirectAddr value in the autodiscover response instead of the RemoteRoutingAddress of a user?