That's what you're looking for! Are you a developer? You don't need us!!! 🙂

Another thing, you won't be able to send mails to nostr people, it doesn't make sense. I would opt for DM or a long form note with your followers quoted at the end.

About followers, as you have already discussed, this data will never be 100% reliable, so these communications will not always reach all the people.

Finally, someone has proposed a mechanism to be able to subscribe to a pubkey and be notified when this pubkey publishes something, this is the right way for me, giving the freedom to each person to receive the information they want.

I see two possibilities, develop the tool or propose a NIP for notifications, both are attractive and can be done in parallel.