Recently, I assisted my colleagues to investigate the server and found that many servers started a process that the development colleagues did not recognize, thinking it was an abnormal situation.
Later, I learned: Centos will start the postfix service by default, which can be deleted to save system resources.
Check whether postfix is enabled:
systemctl list-unit-files | grep postfix
View the listening port of the postfix process:
netstat -tulp
Turn off the postfix service:
systemctl stop postfix
Completely delete postfix related files in CentOS:
yum remove postfix
Reference link: https://www.maixj.net/ict/postfix-20321