The mailing list uses the same 160bit one way encryption of passwords that the forum uses, so should be just as secure.
But if you are using Access as the database and are worried about
hackers getting the list of email addresses from either applications
then you should follow the instructions that come with the applications
of placing the database file outside of your web site to prevent
hackers from downloading the database.
The following article describes how to do this for the forum application, but is very simular for the mailing list:-
http://www.webwiz.net/web_wiz_forums/docs_access_move_ db.asp