Hello!
If suppose we have postfix and have users and some user will send spam, my all mail server will be blacklisted.
Or other situation suppose I have a few mails and somebody hacked one of my mail and know login and password, he will able make remote authentication and start send mail and again my all mailserver will be blacklisted.

How could we protect server from this?

I think it would be well do like it done on opened mailserver like gmail.com. There when you start send mail using their smtp over some account, you instantly get ban, on a few days. You can't send even 10 messages programmatically.

I'm a newbie, have read postfix documentation and can't find there method how to ban users. There only restriction on contents, on recipients, etc. but these are all not what I need.

Who know whether we could do it?