Suppose I add an IP to iptables blocking for exim, dovecot and FTP and this IP visits my server again.
Is there any log of this visit so I can confirm the IP was trying to reach the server again but was blocked?
Try doing this :
If you block a specific IP address (or net) you can view the hit count of the blocking rule via
If you need the information logged you can use the LOG target in iptables:
The first line logs the connection attempt (to syslog or whatever you have configured) prefixing it with "iptables: " so you can grep more easily or have the output redirected by syslog to a special iptables.log for example. A LOG-jump always returns to the chain where the connection attempt is now dropped by the second rule.
Also see @sputnick's answer for additionally rate limiting those log entries to prevent logspam.