Today I have brazen attack to my pop3-dovecot server and mail log is full over (200MB) with this kind of information:
Nov 11 09:28:14 lax dovecot: pop3-login: Aborted login (auth failed, 1 attempts): user=<shawn>, method=PLAIN, rip=200.233.152.111, lip=myip
Nov 11 09:28:14 lax dovecot: pop3-login: Aborted login (auth failed, 1 attempts): user=<shop>, method=PLAIN, rip=200.233.152.111, lip=myip
Nov 11 09:28:14 lax dovecot: pop3-login: Aborted login (auth failed, 1 attempts): user=<sitetest>, method=PLAIN, rip=200.233.152.111, lip=myip
Nov 11 09:28:14 lax dovecot: pop3-login: Aborted login (auth failed, 1 attempts): user=<solar>, method=PLAIN, rip=200.233.152.111, lip=myip
Nov 11 09:28:15 lax dovecot: pop3-login: Aborted login (auth failed, 1 attempts): user=<services>, method=PLAIN, rip=200.233.152.111, lip=myip
I just blocked attacker's ip by iptables
-A INPUT -s 200.233.152.111 -j DROP
But it this can be continued anytime from other ips.
My question is: Is there any method to disallow anyone to connect my pop3 server (except only me?) because my ip is dynamic from ISP side so I don't know how to make pop3 server know that it is exactly me connecting to. Thank you in advance!