Jira Server/DC - when mail polling stops, fixing without a Jira restart

If you see JEMH not processing mail recently, its possible Jira is no longer polling mailboxes, which seems to relate to https://jira.atlassian.com/browse/JRASERVER-62072 , a recent suggestion there that is worth trying to ‘reset’ the mail polling (without a Jira restart) is (from a recent comment):

For the mail queue issue, I was able to get it working again without restarting Jira completely. You can go to Administration > System > Services and edit the Mail Queue service. Don't change anything, just hit update and the mail queue will start working again.