How to view SMTP logs in CentOS7?

Question

CentOS

The server runs on CentOS7, the smtp server is not configured, the mail goes through the php function. The problem is that the mail does not go to mail.ru, gmail, etc., only goes to Yandex, you need to look at these logs, so Yandex support says, where do they look at all?

Answer 1

/var/log/maillog