How do you protect against outgoing spam

[nuke3d]

Hi

I've recently had a new user on my panel that started sending out spam from his e-mail address he created with ispCP. Since I basically every new user has to be regarded as untrusted on my system I'd need some way to filter messages leaving my own mailserver instead of just checking incoming mail. I guess the best way would be to throttle the delivery and maybe run spamassassin on outgoing messages.

I could just add

Code:

check_policy_service inet:127.0.0.1:12525

to the smtpd_sender_restrictions but that would check my server against dnsbls which I don't want.

How do you handle this? Do you know how gmail/hotmail/etc go about this problem?

Thanks for any input