set list-on-separate-pages

SET LIST-ON-SEPARATE-PAGES NO/yes  -  whether to page-break between messages

With the usual NO setting, the LIST command does not put a page break
  (control-l) between messages.  There is a page break between the cover
  sheet and the first message.  You can specify a page break between
  messages by using the switch /separate-pages with the LIST command.

If you change it to YES, LIST will always put in the page breaks.

For more help, type "help" and one of the following:
(at any prompt:)  save-init   set   show   list