Can spamming be stopped?

[Diana Mateja <dmateja @ austin . rr . com>]

I have just been introduced to Majordomo and have been given the task of
stopping the spam messages that are hitting our email lists managed by
Majordomo.  I was wondering if there was a way to restrict the
messages.  We have an open email list because our customers need to have
access to this list but is there a way to automatically screen the
spammers?
Thanks for your help,
Diana Mateja