If you have a single domain, odds are you prefer that your users can log on to Outlook Web Access without having to enter the domain name, which many of them probably don’t even know anyway. For the actual OWA login page, this is simple; See this link for info on changing the default domain property.
Unfortunately, the default domain setting does not apply to the form that allows you to change an expired password. Notice how the login screen only asks for “User name:” but the change password screen asks for “Domain\user name:” And sure enough trying to change a password without using the domain will simply not work. The fix for this is actually simple although it’s a bit of a hack; be careful.
On your Exchange server (presumably your CAS server; we’re in a single-server environment), navigate to {Exchange Install Path}\V15\FrontEnd\HttpProxy\owa\auth\15.0.847\scripts\premium and find fexppw.js. I’m not sure if the “15.0.847” directory will change with patches or service-packs; this is what ours is on Exchange 2013 SP1.
Open the file, and find the below lines:
// Fill in username, set focus to password
//
gbid(“username”).value = rg[3];
Change the last line to:
gbid(“username”).value = “domain\\” + rg[3];
Now the user name field will correctly populate the domain name and your users should no longer need to enter it in order to reset their password.
Trials of a Network Admin 