We knew Facebook was eager for new revenue streams. We just didn't know they were this eager.

If you try to send founder and CEO Mark Zuckerberg a message on Facebook, Mashable discovered Thursday, the social network may offer to keep the message out of his "Other" Inbox — for a cool $100.

In our tests from multiple accounts, it appeared to be the case that users only get this message if they're not one of Zuck's 16 million followers. That, however, could still be coincidental.

Keen Facebook observers will recognize this as a variant on the $1 pay-to-message plan that the social network has been experimenting with for months. The company indicated at the time that it would be experimenting with other prices, so it's possible we're starting to see the fruits of that.

There were sporadic reports in December of Facebook charging various people $100 for the service, but this is the first time we've seen it — and certainly the first time we've seen it applied to the founder.

The "Other" inbox is Facebook's dumping ground for all messages it guesses you won't want to read urgently. It's been controversial for some time, as most users are entirely unaware of its existence — and many have been known to discover messages they really wish they'd read at the time, such as job offers.

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The $1 pay-to-message test was first announced in December, and was described by the company as a test. It allows anyone to message any other person's inbox directly for that one-time fee, whether they are friends or not. It was derided by some users as Facebook spam. (However, it is only possible to receive one such message per week.)

Here's what Facebook had to say in a statement from a spokesperson: "We are testing some extreme price points to see what works to filter spam."

Can you see a situation in which you'd pay the extreme price point of $100? Let us know in the comments.