Question in regards to Email System

Form that sends emails

[dailypress]

I was wondering if anyone has any links or suggestions on how to avoid spams on the email forms.
I have a site that is using "formmail" and would like to make sure visitors do not spam others by basically allowing the visitor to send one email at a time.
also I was wondering how I can avoid softwares from using my system to spam others...

[vincevincevince]

formmail in more recent forms has many built in features for limiting spam - do go through the configuration file carefully