denying mail relay + iptables rule

[Felipe Figueiredo <philsf@ufrj.br>]

Hello,

I get, on an almost daily basis, attempts of use of my mail server as a relay. 
Since it (postfix) only accepts relay from authenticated clients (or from 
local), these attempts are usually logged and denied.

I would like to take further measures and add the offender's ip to a 
blacklist, in a similar way as fail2ban do to ssh, i.e., block access from it 
temporarily.

Does anyone has a hint on how to do this, or if it's already implemented in 
someway?

regards
FF