Progression report about the investigation:
At this moment I can read my hotmail account with Kmail+freepops in openSUSE 11.0.
I used the one-click installation (with a number of dependencies) and have to start "freepopsd &" (as root) after a restart.
This shows that it is possible to read (all?) hotmail accounts with Kmail+freepops in Linux.
In Pardus 2008.1 I downloaded and compiled the source code of freepop with 3 warnings.
Kmail in Pardus (with the same settings as in openSUSE) reports "No new message" when I fetch hotmail.
This is strange and unexpected.
I am now going to do a new installation of openSUSE and try to compile freepops from source.
Maybe this will help to solve this mystery.
Any additional idea is very welcome!