Facebook today announced refinements to its Messaging filters, as well as a test for a very small portion of American users to determine if they'll pay to contact people they aren't Facebook friends with. The test doesn't come at a great time for Facebook, which is in the middle of dealing with a flurry of bad press from changes to Instagram's terms of service earlier this week.

While Facebook messages from friends always hit your inbox, most messages from people you have no mutual friends with get sent to an "Other" folder — a folder most people never check. Under the new test, a person you're not friends with could pay to reach your inbox, and Facebook says you'll only receive one such paid message a week. Facebook hasn't announced a price, but AllThingsD reports it'll start at a dollar and vary as the company tests the service and pricing. All messages between friends, and even in many cases between friends of friends, will still get delivered to your Inbox for free without a hitch.

Facebook's pay-per-message test seems like a clear move towards finding yet another revenue stream, but it's also a strategy to reduce spam messages by erecting a simple barrier between spammers and Facebook users, beyond Facebook's existing automated systems. The company said in a blog post:

Several commentators and researchers have noted that imposing a financial cost on the sender may be the most effective way to discourage unwanted messages and facilitate delivery of messages that are relevant and useful. This test is designed to address situations where neither social nor algorithmic signals are sufficient.

The idea of a social network charging to contact users you don't know isn't new. Popular professional network LinkedIn doesn't let you even attempt to send messages to people you aren't in some way connected to: but its LinkedIn Premium product offers between three and 25 "InMails" per month to people you have no previous connection with. "InMail is 30x more likely to receive a reply than a cold call or email," LinkedIn claims. The difference? LinkedIn refunds your InMail credits if the recipient doesn't respond within seven days.

While Facebook has a much different utility than LinkedIn for most people, there are a few scenarios where you might consider paying a dollar or two to ensure somebody receives your message. Let's say you were sending out invites for a surprise party for a friend of yours, and you aren't friends with all of his or her friends. A message guaranteed to hit a person's inbox could come in handy to make sure even people you aren't friends with receive invites.

There's a real chance that users will see the feature as Facebook charging a toll to reach their inboxes

But paid messaging systems have up till now been reserved for dating sites and professional services like LinkedIn, and there's a real chance Facebook's decidedly more general userbase will see the feature as Facebook charging a toll to reach their inboxes — especially while the company is still battling the negative fallout from this week's Instagram terms of service changes. The small test group combined with the one-message-a-week limit will help — we'll see if this program is enough of a success to be rolled out more broadly.