Search for an email address in Exchange / Active Directory

Open Active Directory Users and Computers. Right click on the domain and choose find. Change to custom search in the find field. Click on the advanced tab to enter a LDAP query.

LDAP query to find the email address [email protected]:
proxyAddresses=smtp:[email protected]

LDAP query to find all objects that uses the email domain domain.com:
proxyAddresses=smtp:*@domain.com