Sep 17, 2018

Why relaying your server mail

A very common way of transmitting email messages in server systems is by sending them directly to other mail servers on the Internet using the SMTP protocol. However, many networks filter outgoing SMTP connections (port TCP/25 outwards). Since default RHEL / CentOS / APS installations will try to send email messages this way, email based alert notifications might not go through as expected in all environments.

This issue is often resolved by making sure that the local mail server sends its outgoing mail through a relaying mail server.