In any case, I added a filter that the relay must have been manually inserted in people's lists in order to display the message. So, most of the NOTIFY from other people's outbox relays are being discared right now.
The only issue is on NIP-50 search. It was added by default for all new Amethyst accounts and that means that if NOTIFY happens and they have the search relay setup, it will display, even though they are not paying for the relay (and most likely don't know what nostr.wine is)