By default, in Exchange 2013, OWA prompts the user to type in their username including the logon name. This can be altered so OWA accepts usernames in a different format.

Change to user name (without domain)

Log on to EMS and run the following Powershell cmdlet:

Set-OwaVirtualDirectory "owa (Default Web Site)" -LogonFormat Username -DefaultDomain your-domain-name

Change your-domain-name to your domain name.

Next, restart IIS to apply the changes:

iisreset /noforce

Change to "e-mail address"

Note: not entirely correct as, in fact, you change it to the UserPrincipalName, which is not necessarily the same as the e-mail address.

Log on to EMS and run the following Powershell cmdlet:

Set-OwaVirtualDirectory "owa (Default Web Site)" -LogonFormat PrincipalName

Next, restart IIS to apply the changes:

iisreset /noforce