linux newbie trying to set up a mail server

Hi,

I have just installed a Slackware 10.2 box to handle mail for my domain
and to run apache with squirrelmail.
I have managed to install and configure postfix to accept the incoming
mail and its dropping all mail into the default location of
/var/spool/mail/user.

I want all mail to be saved in /home/user/mail/box so each user can set
up subfolders in squirrelmail but I can't seem to get the system to work
100% in this configuration. If I get postfix to drop mail at this
location, imapd and popa3d are still looking in the default location.

Is there a system-wide variable somewhere I need to set to say where the
mail is picked up for each user?

Any help will be much appreciated.

Chris.