There's no way to install Outlook on a U3 drive, as far as I'm aware. The
mail accounts go in the mail profile in the registry. Many other settings are
also in the registry. The send/receive settings, toolbar customizations,
default PST folder, and other files are all on the C drive under the
%UserProfile% folder. There's no way to change that, so there's no way to use
a U3 drive.