One must be subscribed to the list before one can send e-mail to the list. This is done in order to preserve privacy. You can verify this by looking at the list of people who are subscribed to your list. If you do not want anyone other than yourself to have the authority to view a list of your subscribers, let me know. The procedure for requesting old messages from a Listserv list is easy.
Archived messages are accessible via the Web for most lists.
Also note that these files can become very large. I suggest that if you need back postings for any period greater than a month that you consider sending one request for each one or two week period during which you want the postings. Listserv has no built in mechanism to manage archived postings for lists. As such, house-cleaning is done on both Listservs only when necessary. This house-cleaning occurs when time permits, but usually it is done at least once each semester when it starts to run low on disk space at which time, old files will be deleted from the server.