There is a website, let's call it domen.com on the server with centos 7. It is necessary to receive an email with an activation link from one service. How can this be done? Here they sent me an e-mail to userdima@domen.com. Where to find this letter? There is a root file in / var / spool / mail, but the required letter is not found there.
There are no control panels on the server, just php-fpm, mariadb, bind, etc. are installed on a clean centos 7. Emails from the server via php are sent normally.
In var / named / domen.com.hosts there is a line:
@ IN MX 10 domen.com. Maybe something needs to be corrected in it. My server, working as root. Tell me how to solve the problem.