Question advanced configure postfix/qmail

[m_145]

Server operating system version

CentOS 7.9

Plesk version and microupdate number

Plesk Obsidian Web Host Edition Version 18.0.59

Hello evryone,
I have many server Plesk Obsidian Web Host Edition Version 18.0.59 installed on centos 7 where qmail and postfix are email sending servers I want to know if I can configure a mail server when only the domains names hosted on the machine can send emails, because some time I have many domains not hosted on the server sending emails using the ip address server.

 

[Kaspar]

How is that possible that domains which are not hosted on your server are able to sent email via your server? How do you know that's even the case?