Recently i bought a Nokia N900 and started right away with configuring my Exchange (Zarafa) account, but i didn’t work.
After making a post on the Z-Push forum i got in contact with Andreas (a Z-Push) and he found out what the problem was. Z-Push implements Exchange 2003 and the Nokia N900 requires Exchange 2007.
Andreas started working on some fixes and after a few days of mailing he made an alpha version which also support the Nokia N900.
At the moment i am running the Alpha in conjunction with my Zarafa envirioment and it works fine, so for all the other N900 users, help is on its way!