Some users may not be able to send emails after the installation of CSF Firewall application. This problem is more frequent among WordPress users, and by setting the outbound SMTP for CSF Firewall using WHM you can solve it.
To Allow Outbound SMTP in CSF Firewall
1. Log in to your WHM root account.
2. Access Plugins from the menu.
3. Click on ConfigServer Security & Firewall.
The CSF application will open.
4. Select the csf tab and click the Firewall Configuration button in the csf- ConfigServer Firewall section.
The ConfigServer Firewall’s configuration interface will appear.
5. Select the SMTP Settings section and click the Off switch for the SMTP_BLOCK field.
6. Scroll to the end and click on the Change button.
It will save the changes you made.
7. Click the Restart csf+lfd button.
It will reboot the CSF application and apply the Changes that you made.
For this reason, the CSF Firewall will no longer block all outgoing SMTP for your WHM/cPanel server.