I checked and found only spam - specifically messages with multiple recipients.
I think FB is using the 'other' folder to avoid brands will notify winners by fb messages.
i have missed a few important messages due t them being i the " other " messages box, its very annoying actually
The possible answers to your survey don't match the question, so the answers are almost as many "other" as "I haven't looked." Not much use.
would be nice if they added an alert or indicator when there is something in the "other" box ...