It just occurred to me, you were not receiving any emails from the forum mail server. I'm wondering if this is somehow related. Somehow the emails were being blocked or filtered out from receiving them. It seemed odd you did not receive any of the test emails sent. The same tests worked for both Birdy & myself. Nobody else has reported registration issues in recent months in regards to not receiving the forum mailer's emails.
Also, you should have received email notifications for each post reply, so you are notified someone has replied to your posts.

Is there something bad about the word gnutella?

I don't suppose Little Snitch has anything to do with email right? Are you using a blocklist with Little Snitch?

I suspect Little Snitch can potentially change the system config files. There might be a change in there which is affecting things. From memory the config files are found in the /private/etc folder, but I might be wrong. Mavericks might be a little different.
Mavericks Gatekeeper might also be an issue.

I'm preferring to stick with Snow Leopard. I don't like having something else control what I wish to open. And the lack of keeping a folder open when opening a sub-folder would slow my work flow down incredibly. Though the work spaces option is good I admit. TextEdit's autosave feature is a PITA & ruined an xml project I was working on. Even the shortcut has changed for selecting multiple random individual files (2 keys instead of one for what should be such a simple task.) If OSX Yosemite doesn't rectify these & some other issues then I'll wait yet a few extra years before upgrading my MP. I get the impression Apple has employed lots of Windows users in its design teams, an OS I hate. lol