centos7 mailx to send mail when ip change

Configuring Certificate Services View:
https://www.cnblogs.com/yunweis/p/8149242.html

Open 25 ports:

First view port 25 situation:

firewall-cmd --query-port=25/tcp

Add Port:

firewall-cmd --add-port=25/tcp --permanent

Overloaded Firewall:

firewall-cmd --reload

send email:

echo "邮件内容" | mail -s "主题" [email protected]