How to block spam email adressess

Since a few weeks some spammers contact my clients, and then, with their answer, send them scam emails directly.
Is there a way to prevent this ? to block some email addresses ?
maybe to let them fill the contact form, but not to send the form ?
thanks

There is an auto reg prevent in the pluggins, it can handle email addresses but unsure if this is connected to the contact response side or just registration ?