Mail List Server
It is absolutely crucial to have a mail list. You want to establish a rapport with your customer/client base. Let them learn to trust you. Be able to offer them new information, products or services. When they need something that you provide you will be the one they turn to.
Most web host providers offer a basic mail list server. If you have a small service company that sends out a monthly newsletter to at most a few hundred clients you MAY get by that.
The best mail list option is a commercial mail list service such as Aweber.
Since mail lists are the sole business of Aweber, they stay current with Spam guidelines, allow you to preview your outgoing mail to see if it will cause any problems, report on the response to your emails, etc. Since your mail list is vital to your business, it is money well spent for a professional service.
NOTE: If you start without a double opt-in list then decide later to move to one, your current subscribers will have to go through the new double opt-in procedure. You may lose 40-60% of your subscribers. It makes sense to start with a double opt-in procedure for your mail list.
