Facebook knows most users don't want another email account that is just going to get filled with spam. So how does Facebook deal with spam? Simple, it puts it into your Others folder.
Otherwise you get users complaining about spam in their messages.
Otherwise you get users complaining about spam in their messages.
It doesn't sound like "Other" was meant to be a spam folder. If that's the case why didn't they just call it "Spam" and install a spam filter to send mail there?
Also if you name the folder Spam, you're acknowledging that the Facebook system can have spam, which is probably something Facebook doesn't want.
Jesus, why didn't any of these anti-spam devices, programs, companies, etc think of it! We'll just make a per user white list and be done with it!
Oh wait, that's a horrible idea, and you should feel bad.
I never said everything in the Other page is spam. I am saying they decided to dump any message that isn't your friend or (friend of friend) into the Others page, which solved for them problem of users seeing "spam" in their Messages page but created other problems.
Either you're going to have a horrible false positive rate or a horrible false negative rate, because sender email address is a really poor feature to determine spam from ham.