Over the past few months I have been using the paid version of Direct Mail, a simple list management program.
Direct Mail is the best mailing list management and mail delivery software for Mac OS X. Its user-friendly interface and powerful mail delivery engine let you stay in touch with your contacts quickly and easily  without worrying about the details of mail server configurations.
I am very impressed with what it does and how it works. The developers are continually developing it so there are updates every few weeks.
A nice effective stable application to aid in sending out newsletter to my friends. Try it yourself.