Adding multiple alternative SMTP Port in Direct Admin

Whereas in Direct Admin, things will done in a manual way. Ssh into the server and type:

vi /etc/exim.conf

Try to find “daemon_smtp_ports” and then you may add/edit the line to look like this:
25 : 587 : 26

The above means the email will pass through only on port 25, 26, and 587

Save and close. Restart Exim.