SMTP Restrictions (WHM) versus SMTP_BLOCK (CSF)

Your new/first Tips, tricks and tutorial forum.
Post Reply
User avatar
Site Admin
Posts: 13
Joined: March 7th, 2022, 1:09 am

SMTP Restrictions (WHM) versus SMTP_BLOCK (CSF)

Post by admin »

Regarding CSF Firewall setting...
and with my experience...

If your core business is related to email marketing...
and got email delivery problems...
which is... emails not delivered and frozen.
while your mail server is in good standing?

Check your mail server status report here:
Mx Tool Box: ... n=toolpage

Virus Total Scanner:

Anti Abuse multi-rbl checker:

and If you've found:
The outbound email issue is happening because SMTP Restrictions are enabled, while CSF is also in use. CSF has its own version of SMTP Restrictions called "SMTP Block", and we recommend using this in place of SMTP restrictions when CSF is installed ... 24mYNdY3DA

If CSF is installed on the server, it is strongly recommended to use its SMTP_BLOCK feature instead of the SMTP Restrictions option within WHM. CSF can remove rules that are not explicitly defined in its own configuration files. As such, rules added via the SMTP Restrictions could be lost when CSF restarts or reloads the rules. In some cases, this could cause problems with all outbound mail.

The SMTP Restrictions feature is controlled through Web Host Manager. When this feature is enabled, only the root user, Mail Agent, and Mailman services are allowed to make outgoing connections over ports 25, 465, and 587. If any other user attempts the connection, it is looped back to the server.

You need to disabled SMTP Restrictions on your server via WHM SMTP Restrictions.

If you have trouble with the SMTP_BLOCK feature, you may want to run the built-in CSF test script to confirm that any necessary modules are installed.
This can be called within your ssh access with the following CLI command:

Code: Select all

Your_root_access@your_device: ~$ /etc/csf/
Or using GUI
Within your:

WHM>> Plugin>> ConfigServer Security & Firewall >> All >> Check Server Security (Perform a basic security, stability and settings check on the server)
Post Reply