Blocking specific users from sending email



We need to block specific accounts from sending emails using SMTP and WebMail. We tried different ideas, but couldn't do it.

We allow users to create test accounts on our server - this process is automated with email confirmation and captcha.

A test account is fully functional for 14 days. For a couple of weeks we are having a spam problem. A spammer keeps creating test accounts from different emails and IPs. Then he uses SMTP and webMail to send SPAM through our server.

This leads to many problems - we keep getting blocked on RBLs etc. We managed to create scripts to block accounts, which send too many emails. We also use ratelimit to minimize the amount of SPAM, but it's still not enough.

The best solution is to completely block an account from sending ANY email until the client makes payment - this guarantees that the account is valid.

Maybe someone has written ACLs to do it? Any other ideas?