I’ve encountered this on my discourse but a while back. My sympathies for what you must be going through! 
I’d not take @codinghorror’s warning lightly - discourse is being developed for the future, and the discourse core team see mailing lists as the past. So at best mailing list mode is a compromise and you will always bump up against difficulties if you try to make it the default way people participate in your community. There are alot of topics about this here on meta you may want to read up on.
That said, there is a way to fix this particular issue, which is to set up a specific category for your embedded topics. You can then mute that category by default for all users using the plugin linked below. That way it will not email people for every new topic created by the embed code.
You can then move topics out of this category as people start talking in those topics as you see fit.