dictionary attacks check

[David Banning]

I just got an email bounce - reason;

The sending IP (162.213.106.199) is listed on https://spamrl.com as a source of dictionary attacks.

The first thing I did was run a check on mxmailbox.com which shows my server as clean from all sites checked.
I wonder what the best way is of checking my system to see if it is commiting these dictionary attacks.

My system it somewhat older;

FreeBSD 3s1.com 9.3-RELEASE FreeBSD 9.3-RELEASE #0

Any pointers would be helpful.