Problem:

Did you ever searched an special email-address in your active directory? If yes, you will know, that there isn’t a special field for the email-addresses.

Solution:

Go to active directory users and computers (ADUC).

Right click on the domain and choose Find.

Select Custom Search in the Find-Field and Entire Directory in the In-Field.

Select the Advanced-Register and type this LDAP query:

proxyaddresses=SMTP:user@domain.com