SMTP restrictions prevent users from bypassing your mail server to send mail.
This feature allows you to configure your server so that the mail
transport agent (MTA), Mailman mailing list software, and root user
are the only accounts able to connect to remote SMTP servers.
Enable from WHM as :
Home >> Security Center >> SMTP Restrictions
When doing so, do you face this error ?
An error occurred attempting to update this setting.
The SMTP restriction is disabled.
When trying to do it from backend,
# /scripts/smtpmailgidonly on
SMTP Mail protection has been disabled. All users may make smtp connections.
There was a problem setting up iptables. You either have an older kernel or a
broken iptables install, or ipt_owner could not be loaded.
In Most cases, the required iptables module, ‘ipt_owner’ would be disabled.
You can confirm it by running
If your’s is a VPS, ask the provider to enable it for you, or if
you manage your server, enable it using the command :
# modprobe ipt_owner