Want to message Mark Zuckerberg on Facebook? For $100, your note will land in his inbox.

Traditionally, if a Facebook user messages someone outside his or her network, the missive gets sent to the "Other" mailbox -- a rarely checked purgatory most users don't even know exists. It's a practice intended to protect users from a spam deluge.

Facebook said in December that it would begin testing out paid messages, allowing users to contact people with whom they have no direct connection in return for a fee. Facebook didn't say at the time how much it would cost, but the answer turns out to be "a lot."

Mashable discovered on Thursday that sending a message to Facebook founder Zuckerberg carries a $100 price tag. That's also what it costs to message Facebook COO Sheryl Sandburg , CFO David Ebersman, and several other Facebook members CNNMoney tried, such as Digg founder Kevin Rose.

"We are testing some extreme price points to see what works to filter spam," a Facebook representative told CNNMoney.

The messaging fee is one of several new revenue streams Facebook is testing out. The company has traditionally drawn most of its revenue from advertising sales, but its latest experiments explore generating cash directly from its 1 billion members.

Ahead of the holidays, Facebook (FB) launched "Facebook Gifts," allowing users to purchase real-world gifts for their Facebook friends. In October, the social network started testing out a "Promote" feature that lets users pay $7 to broadly broadcast important pictures or announcements.