To configure delivery of messages on the server

You need to configure the delivery of messages on the server. Currently letters sent via the website, do not reach mailbox: mail.ru/yandex.ru that is, does not even appear in the spam folder. And if you send letters through the mailbox of the host where the server is, the letters make it to the mail.ru/yandex.ru.

The Server Is Ubuntu, The OpenCart Engine.