Baton Mail 0.9Free
Baton Mail allows you to add mail authentication to your older email clients. Baton Mail is a small application that you run in the background on your computer. You configure your email client to send outbound email to Baton Mail, which in turn performs any necessary authentication with your ISPs mail server, and then relays the outbound mail.
Version 0.9.8b fixed a major bug that caused the computer to freeze when sending attachments.