Running a CPanel server and just wondering what would be the best way to monitor incoming and outgoing e-mail to check for spam and other related attacks.
Currently, I am using exim
cPanel has SpamAssassin support built into it. That's enough for almost all scenarios unless you're doing something unusual.
in addition to SpamAssassin you can use fail2ban to control bruteforce attacks on the server.
look at this howto: Install Shorewall and Fail2Ban on a cPanel server