WHM/CPanel SMTP Restrictions
How to Prevent Email AbuseHow Do I Setup SMTP Restrictions?
SMTP Restrictions (WHM) versus SMTP_BLOCK (CSF)




You can setup SMTP Restrictions by logging into WHM, searching for SMTP (1),
selecting SMTP Restrictions under Security Center (2) and reviewing SMTP Restrictions (3)
Inside the interface, click the Enable button to start the service



SMTP Restrictions is a feature in WHM that stops users from bypassing the mail server to send mail. This service is useful because bypassing mail servers is a common practice of spammers. By setting up restrictions youll only receive mail from root connections, Mailman mailing list software and mail transport agent (MTA) to remote SMTP servers.
Selecting Tweak Settings will take you into WHM >> Tweak Settings where you can also adjust SMTP settings like:

  • Restrict outgoing SMTP to root, exim, and mailman
  • Allow users to relay mail if they use an IP address through which someone has validated an IMAP or POP3 login within the last hour (Pop-before-SMTP)
  • Add X-PopBeforeSMTP header for mail sent via POP-before-SMTP


----------------------------------------------------------------
SMTP Restrictions Disable
----------------------------------------------------------------


Check SMTP Restrictions
This option in WHM will not function when running csf. You should disable WHM > Security Center > SMTP Restrictions and use the csf configuration option SMTP_BLOCK instead
CSF

:
https://documentation.cpanel.net/dis...nt+Email+Abuse
https://docs.cpanel.net/whm/security...-restrictions/
https://forums.cpanel.net/resources/...block-csf.603/