Argh. My incoming email (@pennock.nl which is handled by my ISP and not by my own server) is apparantly experiencing huge problems since I haven't received any email from anyone in the past two days (in comparison to the few hundred per day I normally receive). Test emails I've sent to myself also never arrived.
So if you had sent me any emails in the past two days, I have not received it.
For now, you can send email to "firstname.lastname@example.org" instead (which *is* handled by my own server) until the problem is resolved.