One-way distribution lists can be handled with just an email program. However, if you want to start a discussion list or want to let software do much of the work (such as adding and removing subscribers), you might want to consider a list management/hosting company to tackle it for you. There are hundreds of such companies. Some of them offer free list hosting, others have reasonable rates and others have much higher rates for providing a premium service. Do your homework before committing to a list hosting company. Find out what their policies are (especially for the free offers). Find out what their payment policies are. What will it cost you if your subscriber base grows rapidly. Also research what value-added services they may offer.