It is necessary to extend the Active Directory schema manually so that the mail attribute is returned by an ANR search.
1) Open MMC on a Domain Controller using elevated permissions.
2) Select File | Add/Remove Snap-in and add Active Directory Schema.
NOTE: If this snap-in is not present, run regsvr32 schmmgmt.dll in an elevated command prompt and then try again.
3) In the Attributes folder, find the mail attribute.