Apple Mail likes to prompt about self-signed certificates when connecting to imap or pop servers over ssl. Unfortunately this gets rather annoying after a while so here’s how to import the self-signed certificate into your system.
This is based on a hint from Mac OSX hints but it seems they didn’t quite get a couple of the commands right. Notably the certtool line – you import the .der file not the .pem and you have to make sure you include it from the right directory as well.