The format of this example file /usr/local/lib/poets.list is just a vertical list of mail addresses (one per line).
e.g.
user1@domain1.com
user2@domain2.com
Because the list is not held in the aliases database you don't have to rebuild the aliases database every time you change the list.
You do have to rebuild the aliases database once to get the "aliasname: :include:/filename" line into the aliases database.