Simliar to Outlook, when a user attempts to initiative an email to a user that has turned on their Out of Office Reply- Outlook will provide a proactive message telling the sender that the receiver is OOO and display their OOO message. 

Since there are so many teams that user Confluence as a team calendar- and there is a vacation category....when attempting to tag someone (using the "@" symbol) or assign an issue to someone, can JIRA provide a notification that alerts the user of OOO?