How to Open SMTP Port 25 in Centos 7

If you’re running a mail server or trying to send emails through your CentOS 7 server, chances are you’ll need to open SMTP Port 25—the default port for email transmission. Unfortunately, many cloud service providers block port 25 to prevent spam, and CentOS 7’s firewall settings might also restrict access. This guide will walk you through everything you need to know to safely and correctly open SMTP port 25 in Centos 7.