How do I allow cPanel user to send remote SMTP?

Linux cPanel have many security measurements, in which usually by default we Remote SMTP has been disabled. If you want you can whitelist particular user alone to access remote SMTP.

1. Login to WHM as root
2. Choose ConfigServer Security & Firewall under Plugins
3. Click on Firewall Configuration
4. Choose SMTP_ALLOWUSER and enter your cPanel username
5. Click on Save

Once you allowed the user you can enable remote SMTP access for particular cPanel.