Pleroma supports whitelist (well it calls it accept lists) mode out of the box. we don't include a whitelist though. that's a decision you should make yourself, depending on the needs of your community.

I am working on a mode where you can dynamically add entries to the accept list as new servers are discovered (the so-called greylisting), but this won't make 1.0. OCAP will make greylisting more efficient in the future as well.