Mozilla Thunderbird Portable running on a USB stick?
:?)
 Something like this is what I use at work... 
    Say what you want, but I never
found something so buggy and shitty
 like thunderbird.
    Ok, everyone uses, I never got it to work. 
   I use it all the time, with very
heavy volume.  I have no problems and
 no complaints. (and I have ZERO patience for bad software)