In the past couple of months I have been working on an email archive manager called "AMail" which is written in WPF.
AMail is not an email client, it's only meant to store email messages in an encrypted zip files (using AES256 encryption).
Why not just use an email client?
Well... I find gmail's web interface very comfortable and don't feel a need for a desktop email client. All I want is to be able to store sensitive emails (registrations, passwords, etc...) offline in a protected place in case my gmail account gets hacked, or I forget to log-off someday when connected from a public computer.
AMail allows me to import email directly from gmail (by copy&paste-ing the source of the email) together with all of the attachments.
The project is hosted in Google Code