External SMTP server

Can we integrate an external SMTP server to filter and send mails ??

All incoming will be handled by main server. I am looking so that only trusted and genuine email account will send emails.

Also looking for setting to completedly stop unauthenticated email account to send emails from the server. Not even single mail without authentication will go. Sometime hacked account send mails in bulk.


Take a look → Send emails through Mailgun SMTP on CentOS 7 | birkhoff.me

But it will be costly I suppose.