It's always on.I traced the release notes mention (https://github.com/osTicket/osTicket/pull/3276) I found this commit https://github.com/osTicket/osTicket/commit/f25679ace3d9b485d212bc5303b17aa36ef5ba11Passive Email ThreadingAdd support for threading email conversations happening outside the system.
Autoresponders are paused when threading is on passive mode. Alerts may
still go out to agents as configured.And this: https://github.com/osTicket/osTicket/pull/3419Basically, if you're on the latest code, it's on. The "passive" part appears to simply disable auto-response when a passive-thread is detected. I'm not entirely sure what a passive thread is.. "threading email conversations happening outside the system".. I assume some email clients do something goofy with message headers when replying in threaded mode? It seems to slightly adjust the way the Ticket Thread is identified, adding angle brackets around the email address before searching again. (it's already searched the id by then). You could ask the dev's on those threads though.