Facebook filters many messages to the Other Messages folder (http://betabeat.com/2011/12/return-of-laptop-lost-in-taxi-foiled-by-facebooks-obscure-message-folder/).
Does anyone know how they filter incoming mail to @facebook.com email addresses? Can non-friends email users at @facebook? Can apps?
If the user replies to an e-mail in the Other messages folder, that e-mail address is then whitelisted, and subsequent e-mails will end up in the Messages folder.
I read somewhere that you only have to move a message from Other messages to Messages to whitelist the sender of that message, but that doesn't seem to work.