One day I sent a message via Gmail to Onion Multishop and they answered me the next day, but I understand that it is not good to use Protonmail since that email is closely guarded by the CIA, so I imagine that a seller of that type would not like you. I would give that kind of information to someone, let alone by Protonmail. If Tormail could be used, I think sellers would respond to messages faster but currently Tormail is already dead.