(WHM >> Home >> Security Center >> SMTP Restrictions)
This interface allows you to configure your server so that only the mail transport agent (MTA), Mailman mailing list software, and the
root user can connect to remote SMTP servers. This will deny other users and services the ability to bypass your mail server to directly send mail, which is common practice for spammers.
To set the maximum number of simultaneous incoming SMTP calls, update the smtp_accept_max setting in the Advanced Editor section of WHM's Exim Configuration Manager interface (WHM >> Home >> Service Configuration >> Exim Configuration Manager).
Manage SMTP restrictions
Click Enable to deny users the ability to bypass your mail server to send mail. To allow users the ability to bypass your mail server, click Disable.