This interface works as guidance for your server configuration such that the mail transport agent or MTA, Mailman mailing list software, along with the root user is allowed to connect to the remote SMTP servers.
The objective is to prohibit other services and users from bypassing your mail server to send mails directly. Spammers commonly practice this, and thus, the essence of this interface is to keep spammers away.
SMTP restrictions can be found in the path (WHM >> Home >> Security Center >> SMTP Restrictions). It is of primary importance that you have access as a root user to WHM.
Spammers try to work around the settings of mail security in order to achieve their goal. They communicate directly with the remote mail servers. The objective of SMTP Restrictions in WHM is to prevent spammers from doing so. The user can gain access to this feature from two given locations. They are given below.
It can be found under the ‘Mail Tab’ in the form of an option as ‘Restrict outgoing SMTP’ to ‘root’, ‘exim’, and ‘mailman’.
You can also make use of Tweak Settings and utilize the ‘Mail’ section to make sure of further changes to the existing configuration.
Management of SMTP Restrictions can be done using the given steps.
Once the user enables the setting, it restricts email connections that are going out to the mail transfer agent or MTA, the mailman system user, and the root user.
In the end, both the scripts and the users are forced to make use of Exim’s Sendmail binary instead of gaining access to the socket directly.
One should take note that this particular interface functioned to simply obstruct any attempt to establish a connection to a remote mail server before version 11.32. Eventually, with WHM version 11.32 and cPanel, the software makes it a point to redirect the attempt for connection that goes out to the local mail server.
Thus, this document establishes SMTP restrictions and the reason for its use.