blocking spam IP with netfitler good idea or not ?

[Giuseppe De Nicolo']

Hi,

    I have a question for you more experienced admin ,  I have some 
good abuse on my servers by IP listed in spam list , since I am using 
postscreen to block those all is good ,  anyway I thought then a good 
idea to just drop that traffic and avoid myself thousand of log line 
with 450 4.7.1 service unavailable , ans so I added fail2ban to the 
mix,  inserting those IP into netfilter as reject. Pratically I am 
sending into iptables all the IP which attempt consecutive ( 10 in 600 
sec ) directory harvesting hit and IP which attempt consecutive ( 10 in 
120 sec )connection from spammy IP , the only drawback is obviously that 
I do not see them in postfix log , and so decided to ban them for 3 hours.

    Anyway I do wonder if this is a bad practice and as such should be 
avoided or not ?

Best Regards