Journalists who use Facebook to communicate with sources or their audiences may be missing out on a lot of messages.

The "other" folder collects messages from anyone who's not a Facebook friend, but most users seem not to know that.

As pointed out in a recent Slate article that started a chain reaction of “I can’t believe I didn’t know this” comments, Facebook diverts some of a user’s incoming private messages away from the inbox to an “other” folder. But the user has no idea a new message arrived, or that the folder even exists, unless she goes looking for it.

The result is a black hole of communication that could cause journalists some problems. It’s increasingly common for reporters to find and reach out to potential sources, especially non-official sources, through Facebook. A source or reader also may send a journalist a tip or correction via Facebook message. Now we know some of those messages go unseen, especially if the sender and receiver are not friends on the network.

I posed some questions to Facebook’s press office about why this submerged inbox exists, and if the company will improve the feature (I've added their reply below). It seems to me the problem stems from Facebook’s rollout earlier this year of a new messaging system including a “social inbox.” Here’s how the company explained it:

It seems wrong that an email message from your best friend gets sandwiched between a bill and a bank statement. It's not that those other messages aren't important, but one of them is more meaningful. With new Messages, your Inbox will only contain messages from your friends and their friends. All other messages will go into an Other folder where you can look at them separately.

Facebook saw this as an improvement over the noise and clutter of the all-in-one email inbox. But if you give people a messaging system that looks like their email, they will expect it to function like email unless repeatedly told otherwise.

Until this messaging system gets fixed, journalists should remember to periodically check their “other” folder for messages, and be prepared to use other contact methods to reach sources -- Twitter, email or the old-fashioned phone call or knock on the door -- if you don’t get a timely response on Facebook.

Update: A Facebook spokeswoman replied to my questions, affirming the information I quoted above and offering this as well: "Your Other folder contains messages sent to mailing lists and broad distribution groups, along with messages from people who aren’t friends or friends of friends. If you see a message in Other that you’d like to move to your main messages view, simply open the message and select "Move to Messages" from the Actions drop-down menu." No word on future changes.