@Mention handling
@mentions in Server/DC and Cloud are all internal to Jira and do not follow the IssueEvent pattern. As such, JEMH cannot intercept them, and we cannot customize them. Notifications come from the main Jira mail account as there is no way to do otherwise
What JEMH/C does
We do in cloud what we do in server, which is to detect the presence of an @mention in comments, and inhibit notifications for the party concerned to avoid duplicate content notifications.
Atlassian do not provide a way to disable @mention notifications AFAIK.