The SMTP tweak will prevent users from bypassing the mail server to send mail (this is a common practice used by spammers). It will only allow the MTA (mail transport agent), mailman, and root to connect to remote SMTP servers.
1 To access the Server Setup Menu, click on Server Setup, on the main screen of your WebHost Manager interface. Then, click on Tweak Security.
2 Click on Configure in the SMTP Tweak section.
3 Click on the check box next to Allow connections to localhost on port 25 to allow users to connect to localhost on port 25.
4 Click on Enable to enable the SMTP tweak.