Vertical Response offers approved 501c3 charities 10,000 free emails a month with no monthly fee or contract. And they include full statistics unlike some of the other non-profit offers out there. They also offer easy to use templates and member management options.
In addition, VR offers a very inexpensive option for allowing people to buy tickets to events or chance drawings. We all know every penny counts when you're an all-volunteer rescue group and it's pretty rare to find a no strings attached deal so this is a pretty cool company. Check Them Out!