This is the new DM I am working on: https://github.com/nostr-protocol/nips/pull/686 and it is available on Amethyst right now. It tries to be as private as possible without having to have an AUTHed relay. I would argue that in extreme privacy implementations it could be more private than SimpleX. A client can have a DVM to connect to receiving relays for users and not leak your device's IP that would allow for some correlation even if everything is encrypted. 

nostr:nprofile1qqsrmpp2lmx4u2fl9zmxy7fnwp9rlwxwz5a2j8tep2c376n494z2gtgpzamhxue69uhkjmnzdauzumn0wd68ytnhd9hx2tcprpmhxue69uhkxetvd3shytnwdaehgu3wwa5kuef0qyghwumn8ghj7mn0wd68ytnhd9hx2tcwamxyd  has a very good start with inbox.nostr.wine. The way to see the relay is as a mail box for the user. The user is paying for the relay to receive and store any event that `p`-tags the user. They might be spam or real messages. It's not the relay's job to decide which is which. It's the user's job (via a good client that helps you manage your inbox) to delete things that are spam and clean up their account with the relay from time to time.