Postfix suddently stops logging on CentOS 7

Postfix keeps on working but suddenly stops logging.

tail -f /var/log/maillog shows nothing.

Eventually you discover that Postfix is now logging to the journal.

To see the full log:

journalctl -u postfix

To clear the log:

journalctl --vacuum-time=1d

To tail to log:

journalctl -u postfix -f

Reference:

https://unix.stackexchange.com/questions/165201/postfix-no-longer-logs-to-var-log-mail-after-it-has-been-deleted-and-re-created

https://unix.stackexchange.com/questions/139513/how-to-clear-journalctl