It is my understanding that many E2EE chat systems won't actually E2EE your initial message to someone you aren't already mutual in-app contacts with.

Either E2EE is something you "upgrade" an existing conversation into (only after both sides consent to the conversation); or E2EE is something that only inherently establishes once both sides have sent one-another a message; or E2EE is something you can only enable before you start a conversation, if you already have the other person's public key (which you only get when you request to add them as a contact, and they accept.)

I think schemes like this balance privacy with spam-prevention quite well: privacy-conscious people can explicitly add each-other before either person says anything / can send intentional small-talk as pairing messages; while everyone else gets the benefit of a central spam-filter sitting between them and messages from strangers.