There are a lot of "hostname ... does not resolve to address ..." in mail.log. Yesterday: Code: Warnings -------- smtpd (total: 1254) 606 hostname 77-105-44-25.adsl-2.sezampro.rs does not resolve to ad... 30 table "mysql:/etc/postfix/mysql-virtual_client.cf": empty query... 14 hostname 188.8.131.52.broad.wz.zj.dynamic.163data.com.cn does... I thought to use fail2ban, banning them for a while. But seems there are no filters I can find to do that. Before writing my own filter, is this banning not a good idea? I assume if it were without bad side effects, fail2ban would already have suitable filter to ban these somewhere.