There are many an Exchange environment that requires people to add a domain setting when configuring ActiveSync settings on mobile devices. This may be due to the fact that there are multiple forests or domains in an Exchange environment, this may be due to the fact that Autodiscover isn’t working properly or something it may be a configuration problem with how IIS (Internet Information Services) are configured on a server. You probably don’t really care why you need to throw the domain in the Email Settings, just maybe how you go about it.
Learn To Add Your Domain Name To Email Settings On The Bushel Blog…