[imp] https problem

[mathias]

hi all
i have somewhat successfully set up a webmail interface for our school using
horde/imp, and apache.
the problem is, when i try to run it over ssl, the pages after the login
page are unencrypted (or not found, if i set up the webserver to use only
https://).
have i set up something wrong? is it a php problem? even if i explicitly
load https://securemail.xx.ch/horde/imp/redirect.php (in login.php), i still
get the pages unencrypted.
i can redirect all http traffic on this server to https, but i still get
annoying messages in style with 'you are leaving the secure sector...'
(although i'm not, i think).
i can't be the only one who wants this setup. can anyone point out to me,
what i could do to fix this, please

thanx

mathias