Ca marche pas.

Donc ruse vue sur le forum Zimbra, elle même piquée chez Kerio :

Disable certificate checking in Windows Mobile 5 device by editing following registry in Hkey_Current_User\Software\Microsoft\ActiveSync\Partners\UID_Server_partnership.
Add a new Value secure of DWORD type and set it to 0.
UID_Server_partnership is unique ID number specifing the partnership with the specific server.