Thunderbird Portable, real email, on the go™ - Mozilla Thunderbird -
Portable Edition is the popular Mozilla Thunderbird email client packaged as
a portable app, so you can take your email, address book and account settings
with you. You can also get it with GPG and Enigmail preconfigured to encrypt
and sign your email. The portable version leaves no personal information
behind on the machine you run it on, so you can take your email and adress
book with you wherever you go. (in Internet)