-- deleted user
-- Active Directory
-- LDAP

User account has been deleted in Active Directory but Mailgate can still find the user. Therefore, email is still being accepted for a user who does not exist in Active Directory.

The only reason why Mailgate can lookup the user is because the email address still exists in Active Directory.

To locate this email address you can use a LDAP query tool and it will indicate where the object is - it may be in fact located in a hidden OU. After removing the object that contains the email address, the LDAP query tool should return 0. Mailgate also will not find the email address anymore

Please also make sure that the user is not in your local users directory or LDAP replica. You may use the user search under Administration > Users to ensure where exactly the record is found