This?
Do we have a NIP for tracking read/unread messages between clients? nostr:npub18m76awca3y37hkvuneavuw6pjj4525fw90necxmadrvjg0sdy6qsngq955 nostr:npub12vkcxr0luzwp8e673v29eqjhrr7p9vqq8asav85swaepclllj09sylpugg nostr:npub1nz64zngcqm8vj8nhrdkcjpfwn2rcaqysnxec88tqfclp5afrpglsqm0w5y nostr:npub1tm99pgz2lth724jeld6gzz6zv48zy6xp4n9xu5uqrwvx9km54qaqkkxn72
Discussion
Looks like the kind of thing. No privacy issues with this approach for private messages?