Something wrong happened in my dad's Evolution. It just would get stuck checking mail forever, with no useful diagnostic that I could find. Fun. Not.
Anyway, I solved by resetting everything to factory defaults, moving away all gconf entries and .evolution/ files. Then it started to work again, of course then I needed to reconfigure it from scratch.
It turned out however that some old mail was only archived locally, and in a kind of weird format that looks like this:
$ ls -la Enrico/
total 336
drwx------ 2 enrico enrico 4096 Jul 23 03:05 .
drwxr-xr-x 7 enrico enrico 4096 Jul 23 03:12 ..
-rw------- 1 enrico enrico 3230 Dec 4 2010 113.HEADER
-rw------- 1 enrico enrico 14521 Dec 4 2010 113.TEXT
-rw------- 1 enrico enrico 3209 Oct 22 2010 134.HEADER
-rw------- 1 enrico enrico 2937 Oct 22 2010 134.TEXT
-rw------- 1 enrico enrico 3116 Jun 27 2011 15.
-rw------- 1 enrico enrico 3678 Jun 27 2011 168.
-rw------- 1 enrico enrico 73 Apr 27 2009 22.1.MIME
-rw------- 1 enrico enrico 3199 Apr 27 2009 22.2
-rw------- 1 enrico enrico 88 Apr 27 2009 22.2.MIME
[...]
I couldn't even find the name of that mail folder layout, let alone conversion tools. So I had to sit down and waste my sunday break writing software to convert that to a mbox file. Here's the tool, may it save you the awful time I had today: http://anonscm.debian.org/gitweb/?p=users/enrico/evo2mbox.git
Note: feel free to fork it, or send patches, but don't bother with feature requests. Evolution isn't and won't be a personal interest of mine. Anything that makes an afternoon at my parents more tiresome than a whole busy month of paid work, doesn't deserve to be.
Luckily they now seem to have changed the local folder format to Maildir.