Any OpenSource Email Marketing Software ?

3x WHM VPS + Growing
G'day all,

I am trying to find some open source email marketing software. We have a client list we can load into a DB and need to use template(s) to send regular mails to our clients and of course the yearly happy holiday email. Anyone recommend anything ?

By the way. THANKS KnownHost for our Christmas card, most impressed a US business bothers to send to us Down Under.

Happy Hols to Known Host and all the happy customers :)

Sydney, Australia