If a user is on the notification list for a Jira issue and has set an automated out-of-office response their OOF message will auto-post as a comment on the Jira issue. You can find the behavior demonstrated in JRA-4052. I fear that if two users both set Outlook to send automated out-of-office responses and don't set the responder to not reply to replies then an escalating cascade of automated responses could flood the server with useless comments.

Unfortunately, I don't have the complete backstory and all the details about the systems involved, but the effects can be seen in JRA-4052 and the user with the auto-response is yazhou.