if they're to root and anonymous it's a good chance they're status messages that aren't actually getting anywhere and are sitting in the queue being deferred until they eventually die. If you have lots of things on your system happening for which there are status messages being generated, they can very quickly add-up. The way qmail splits up its storage of each message into 3 files just exacerbated the problem and inode depletion can happen, as you're seen.
you can check how many email are in your queue with qmail-qstat
First and foremost i'd create aliases for root and anonymous that go to your address so that you can receive these status messages:
I'm guessing r33422.ovh.net isn't the mail domain you're using, but that's the domain to and from which the messages are being directed. if that's the name of your qmail box, you much change /var/qmail/defaultdomain to be the domain you're using for email and the aliases should just start working. If that's a different host, you can either change the defauldomain on outgoing mail, or create a virtualdomain on the qmail box so that it accepts mail on behalf of r33422.ovh.net and then forwards it to you.
Getting that done should solve your immediate problem because your queue will clear out in a hurry.
Next, if you ever expect this box to have lots of mail on it again, you should look at mounting a new disk or partition for your queue directory and make sure you format it with a small inode size. What's happening is that you have lots and lots of small files, probably less than 1k each, but maybe 4k or 8k or 16k inodes, and each tiny file takes up an entire inode... so you can run out of allocatable space even though you have plenty of unused space on the drive.
Worst-case is that someone is hijacking your mail form and sending out spam on your behalf and the status messages in your queue are failed bounces. You'll definitely want to get you hands on those messages to determine if that's the case and take further actions if necessary