Windows 2008 R2 Domain Login with Email Address

I just started at my company and trying to understand the following:

Our internal domain is: but our email address for our company is

Under ADUC, there is not an option for additional DNS suffixed for UPN login. With this in mind, how is it that users are able to log into the domain using there email address?

Nothing is listed under AD Domain and Trust as well...

There is no parent company.
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Will SzymkowskiConnect With a Mentor Senior Solution ArchitectCommented:
AD is your internal domain name and the is usually your external registered Domain Name. In Exchange this is populated from the Email Address Policy. You can give you users any UNP suffix can be anything but your Exchange is usually different than your internal domain name as this is split brain DNS.

Mike KlineCommented:
You can add the UPN suffix

Then you can select that for your users in their account properties.


compdigit44Author Commented:

I am just confused it users can log into our internal AD domain with their email address if the UPN / domain suffix is not an option under the UPN drop down in ADUC... This is why I am confused???
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