Hey, I built an SMTP server on Centos 7 VPS using Webmin and I installed Mailwizz Application, But when I want to add my server to Mailwizz I get this message Connection could not be established with host mail.domain.net :stream socket clie...

I built my server on contabo using Webmin and installed mailwizz but when I add my SMTP to Mailwizz and want to validate it I keep getting this error below. I even tried switching between SSL and tls and none and nothing changed. Connection...