[CentOS] Mail has quit working

Tue Jul 24 14:31:43 UTC 2018
Gordon Messmer <gordon.messmer at gmail.com>

On 07/23/2018 03:39 PM, TE Dukes wrote:
> Mail has come to an abrupt stop. Running C7, postfix and dovecot.
> ...
> Crond is no longer send mail.

In one terminal: "tail -f /var/log/maillog" or "journalctl -f"

In another, "echo test | mail -s test your at email.address"

What do you see in the maillog at that time?  What does the "df" command