[CentOS] Dovecot under brute force attack - nice attacker

Hi List,

optimizing the configuration on one of our servers (which was hit by a brute force attack on dovecot) showed an odd behavior.

The short story: On one of our servers an attacker did a brute force attack on dovecot (pop3). Since the attacker closed and reopened the connection after every user/password combination the logs showed many lines like this: dovecot: pop3-login: Aborted login: user=<test>,......

The problem: If the attacker wouldn't have closed and reopened the connection no log would have been generated and he/she would have endless tries. Not even an iptables/hashlimit or fail2ban would have kicked in.

How to reproduce: telnet dovecot-server pop3 user test pass test1 user test pass test2 ... QUIT ->Only the last try gets logged.

Question: Is there any way to close the connection after the first wrong user/pass combination. So an attacker would be forced to reopen it?

Any other Ideas? Henry