The Mobility Email Client is a freeware portable email client for Windows that can be run off any portable drive such as a USB key. It does not require any installation nor does it store any configuration information on the drive or in the registry. Just plug in your portable drive, check your emails and disconnect the drive without leaving any information behind.

The Mobility Email client works with any email protocol such as POP3, IMAP4 for recieving emails, SMTP for sending emails, RSS feeds or HTTP based webmail service providers such as Windows Live Hotmail, GMail, AOL and Yahoo!. It also supports S/MIME and OpenPGP for securing and encrypting emails that are sent out.

Download here

Warning: The email client is almost 18MB in size.