Options for Recipient Verification
====Active Directory/LDAP:====Yes, sure. Please go to Setup->User Lookups. From there you can create an LDAP user-lookup that will be used to look up email addresses. (See the Online Documentation for details.)
If you only want the LDAP lookup to check for the existence of an email address, but not to set the stream name, then when you create the user-lookup, set the "List of attributes to use for stream name:" to some nonexistent attribute and set "Action if stream attribute missing:" to "Use email address (AsIs)"
We have a training video on LDAP lookups: http://www.roaringpenguin.com/resources/videos-ts/configuring-ldapad