Thanks Pondus, I watched the video and did all what it said, but still it does not work. It still does not receive mail, and stops with the message that the connection expired.
DavidR, I reset the ports to the default ones Thunderbird mentioned when watching the video both of you provided, it still fails to work, see above.
EDIT: Woops, failed to see the difference in links. I'll go check out DavidR's link in a moment
EDIT2: Works now, thanks!
Thunderbird doesn't show the last number of the default port, so I entered 14 instead of 143 at IMAP. Thanks for the help guys!