Question: Am I allowed to use formmail.pl?
No! Spammers have tools that search sites 24/7 for this script. It's just a matter of time before they find it and start using it to send out vast amounts of spam.
Instead, use a php version. You can find good examples and even a wizard to generate a script here: http://www.thesitewizard.com/wizards/feedbackform.shtml