Change the OWA login from “Domain\UserName” to just “User Name”. This is useful when you have Single Domain Exchange environment.
Find current logon format:
Get-OwaVirtualDirectory -Identity "owa (default web site)" | Format-Table OwaVersion,Server,LogonFormat,DefaultDomain -Auto
Set logom format:
Set-OWAVirtualDirectory -Identity “owa (default web site)” -LogonFormat username -DefaultDomain “Your Domain Name”
ISS Restart: IISRESET /NOFORCE