>It's open in the sense that anyone can use it. Without restriction. And there's no way to be banned from it. Since anyone can just drop off an anonymous letter in the post. You don't have to enter a service agreement. Just dump you satchel of letters with stamps on them, in the nearest mail box.

1. So this sounds like the section 230 debate all over again? eg. "Facebook can ban people from facebook messenger, so if they're not banning scammers they should be on the hook for it"?

2. What about ISPs? The internet might be open, but ISPs certainly aren't. People get banned for AUP violations or alleged copyright infringement all the time. If ISPs reserve the right to ban users for various ToS violations, should they be on the hook of scammers turned out to be using their connection?