[CentOS] Mail has quit working

Tue Jul 24 01:42:58 UTC 2018
Bernie Pannell <bernie at sterland.com.au>

> Did the telnet localhost 25, it answered but not sure I understood you
> what I needed to do.

​type all this in once connected, substituting as necessary & ignoring the
comments in ()

helo mydomain.com (substitute a valid domain here)
mail from: <someuser at validdomain.com>
rcpt to: <youremailaddress at yourdomain.com>
From: someuser at validdomain.com
to: youremailaddress at yourdomain.com
subject: test
  (note blank line here)
This is a test message