blocking IP based on hits

[dave]

Hello,
    I've got an ipfilter firewall also providing nat services. It forwards
email to a natted smtp server. This email server is repeatedly getting hit
by IP's atempting to spam it. I was wondering if it's possible either on the
gateway machine or the email server, both are running ipfilter to drop an IP
say for example 192.168.111.222 if it hits, is dropped, reconnects, and so
forth, x times within say a given minute?
Thanks.
Dave.