Combine mail enabled and disabled groups via group nesting

Greetings,

  Can anyone point me to a document that describes the rules for combining mail enabled and disabled groups via nesting?

 For example, user is a member of GROUPA which is not mail enabled and GROUPA is a member of GROUPB which is mail enabled so if I send mail to GROUPB does the user get it? Do all the groups in the nesting chain have to be mail enabled?

Thanks

David Z