Linux Send Mail Transport Protocol Vs cPanel SMTP Tweak.

[admin]

As a Linux/Unix user,
In my experience...

On Dedicated server...
As for "SMTP Tweak" in WHM, I would strongly recommend using CSF Firewall instead of "SMTP Tweak" in Cpanel, However, you can use neither of these if your base iptables is not working on your server since both CSF and Cpanel's SMTP Tweak are based upon iptables at least being installed and functioning correctly within Exim configuration.
Pretty Fast and Responsive, Secured and Stable!

On VPS server...
On Virtuozzo or OpenVZ, the necessary modules to use iptables might not have been configured. You might want to talk to your VPS provider if that's the case where you are on a Virtuozzo or an OpenVZ environment.

Aside from being extremely bad at managing VPS resource allocations, it has several really huge security holes which by it's core design could never be fixed or patched and also leaves the final end user very limited in the amount of control, So you need to be more creative. For security reason, just don't forget to setup spamd startup configuration and monitoring your server status routinely regarding spamd(spam daemon) service status and your mail server will be fast, stable (Load avg, CPU us, Memory cons, etc.) secured and protected from email spoofing attack.

Last but not least... don't forget to backup your my.cnf (MySQL Configuration) and exim (MTA) configuration.