CommuniCrypt Mail
Standalone eMail client with built-in strongest asymmetric Public-Key-Encryption with RSA encryption algorithm (RSAES-OAEP). Key length for encrypting up to 7120 bit. This eMail client is fully featured for receiving/sending mails via POP3/SMTP. With the integrated SMTP engine you do not need a... Other features: mail forwarding, mail repying, a little addressbook, encryption optional, attachments(encrypted with RSA or AES Rijndael), key compatibility with other CommuniCrypt products, minimizeable to tray, online update and much more!
http://www.communicrypt.com/downloads/ccm_setup.exe - 5Mb - Download - Screenshot

CommuniCrypt2Go
RSA encryption tool for eMail-, webmail & messenger communication. No installation required, should run from an USB-Stick and other temporarely devices. See www. communicrypt. com for details.
http://www.communicrypt.com/downloads/cc2go.exe - 370Kb - Download - Screenshot