How do you rate limit outgoing mail per user in Postfix?
Answer
Use Postfix parameters like smtpd_client_message_rate_limit, smtpd_client_connection_rate_limit and smtpd_client_recipient_rate_limit, or a Postfix firewall like Postfwd. Rate limits cap the damage when a user's password is sniffed or a customer's computer catches a virus.