In my experience most forums have private messaging.

Additionally I think it is fine to say "we don't support e2ee". I prefer honesty to a bad (leaky) e2ee implementation, at least the user can make an informed choice.

I agree. At least take of "Yes messages are stored on our servers" is honest. And if they are accessed by anything else than limited subpoena is policy or legal issue.

>In my experience most forums have private messaging.

Yeah but it's kind of accepted that the forum owner could read it all if they so chose. Maybe this is a hold over from back in the old days when encryption was nowhere near default during which forums arose.