The Postfix feature you want is called "anvil".

The anvil(8) server implements client connection and request rate limiting
for all smtpd(8) servers. The TUNING_README document provides guidance for
dealing with mis-behaving SMTP clients. The anvil(8) service is available
in Postfix version 2.2 and later.

Reference: man anvil

--
Greg



Q wrote:
> Hi guru's...
>
> Problem: (public) webserver with malicious mailscript was used to send
> (spam) mail.
> Is there a way to prevent this from happening??
>
> e.g. limit postfix to send only 1 mail per second...
> Have been digging the smtpd_recipients options etc, but can't figure out the
> best way..
>
> Help is much appreciated.
>
> Kind regards,
> Marco
>
>