@davidbrown You are welcome.  I think that it was designed this way also, to be GDPR-compliant and CAN-SPAM Act - compliant, as Forum Admins, we always have to give our members that option to either subscribe to or unsubscribe from Forum topics, but they have to "Opt-In" and subscribe themselves, and not automatically be subscribed.  🙂

If it is automatically set to send, each and every time someone responds to a forum thread (especially for some trending topics on your forum), your website will also be automatically sending out auto-emails which might cause your domain name to be "flagged" as sending spam if it's sending out too many automated emails originating from your domain.  Just another insight.  🙂