Thunderbird Portable
On my main PC I have my normal installation of thunderbird (and Firefox) on the other PC I have a basic windows setup and several Virtual Machines setup for Linux and other XP testing VMs. I don’t have Thunderbird installed on this machine instead I use Portable Thunderbird
Mozilla Thunderbird™, Portable Edition is the popular Mozilla Thunderbird email client as a portable app, so you can take your email, address book and account settings with you on your flash drive. This Portable Thunderbird is a copy of one I carry around with me on a flash drive. For safety sake and in case I loose the flash drive Thunderbird Portable is hidden inside a Truecrypt encrypted container.(This software is recommended for securing data on laptops or flashdisks.) This Thunderbird Portable has my ISP email details, hotmail, yahoo and my work email account and my encrypted emails. Oh and another copy of Thunderbird Portable on my work PC.
The big problem here is that I have at least 3 copies of Thunderbird active at the same time, so quite often they have different files on each, all of which I want to keep.
I use synchingthunder which works really well, but seems to be sporadically maintained hope this guy keeps up the good work.