Nopc
From xat wiki
(NOPM) - Tylko odbierać PW od znajomych
Powers nopm umożliwia blokowanie wiadomości od użytkowników, którzy nie dodali.
This also means if you private message a user and you have NoPM enabled and you don't have them added, they will not be able to private message you back.
Note: Chat staff and xat staff can always private message you.