Uncheck the textbox below the comment field:

I'm looking for a more permanent solution. 

It's unchecked until you check it yourself, seems quite permanent to me.

On the top where the thread heading is located, enable/disable it by toggling "Follow" or "Unfollow"

Eh, I seem to have fixed it in my settings.  But after adjusting those settings, I received emails about threads I'd posted in before.  

Haven't gotten any emails since, though.  

I've never actually checked the box asking for notifications.  

I can't say I'm overly fond of the new setup.  

The only change we've made recently to the way that email notifications work is that we've added email notifications when someone responds to a specific comment you've made. As this is a response directly to you, these automatically give you an email notification because it's a personal response. 

Regarding email notifications for comments, in general, this works the same way it's worked for years. If you want to get notifications when other people comment (or stop getting notifications), click the "follow/unfollow" link at the top of the thread, or check the notifications opt-in box when posting a comment. Notifications are never enabled by default, but Archinect will remember your preference, so if you check the opt-in box when posting a comment, that box will be auto-checked the next time you make a comment, but you can uncheck it and that preference will be remembered going forward. 

When you get an email notification, there's a link in the email allowing you to immediately stop getting notifications for that thread. If you stop opting in to comment notifications, and unfollow threads you are currently following, you will stop receiving them.