Yesterday I blocked 1300+ attempted connections from spammers using the excellent Spamhaus project for a client who relies on me for e-mail solutions.
Checking for rejected mail hosts: 1131 .net (550... zen.spamhaus.org) 159 .com (550... zen.spamhaus.org) 35 .com (550... zen.spamhaus.org) 35 .com (550... zen.spamhaus.org) 3 .com (550... [189.106.24.47]) 1 .com (550... [123.64.195.52]) 1 .net (451... resolve) 1 .com (550... [79.142.108.9]) 1 .com (550... [59.92.118.222])
I use FreeBSD 7.2 with Sendmail, configured to use Spamhaus to do IP lookups and milter-greylist as a second line of defense.