Changing users home massively

Hello, do you now a quick way to change the home of ALL users at the same time except the system users ? I'm running on a m00b trouble with a mail server, you know . . . /var is too big and local directories are at /home so /home needs space too . . as a mail server, my approach now is to move all the homes to /var.

Thank you.
Boot into single user mode, move /home to /var/ (so it becomes /var/home) and symlink /home to /var/home. This will not affect root (which is in /root). 'System' users have no home directories (usually /var/empty or /nonexistent).