A sublist is a list that receives its input from another mailing list, rather than from users directly. The sublist is just a regular subscriber of the main list. A sublist in e.g. Tasmania is very useful since only one message is sent from the main list and then the sublists servers all subscribers in Tasmania. Bounces and all administration is handled locally. The local sublist can have a digest, even though the main list may not. See How sublists work for more information on how sublists work.