One of the tools to avoid email spam is Relay Block Lists (RBLs) and although it’s not perfect, it can be a great help to block the most obvious cases of spam/abuse.
The other day I was looking into the RBLs I am subscribed to for an email server I run and thought that maybe a similar feature could work for Mastodon.
An RBL like could be a good fit because it is not a fully centralised, you may subscribe and unsubscribe to as many RBLs as you like, like the current Mastodon Relays.
I am just sharing this here to know what your opinions are on this and what could be problematic with this approach.
There are several ways this could be implemented in terms of where the RBLs are server, either using external software (like the current Mastodon Relays) or internally and included in Mastodon. In my mind an internal solution would be great because each instance could be an RBL.
Example: my instance already has domain blocks and email blocks, if you subscribed to my instance RBL then you would also be applying the same domain and email blocks.
Obviously there should be an option to make your instance an RBL (make your blocks public) or not.
I don’t think this would bring a great overhead, as RBL update frequency could be very low (like once every 24 hours or something, no need for realtime).
This could be a great way to reduce moderation needs and also reduce registration spam as the problematic emails would rapidly reach instances.