Your customers need to hear from you. They need to know what you have going on - sales, new products or services, special events, etc. for your business. They also need to see that you are an expert in your field, so you need to share with them when you learn something new or hear about something that might be of interest to them.
There are a lot of email marketing tools available, but I recommend Constant Contact. It's priced very reasonably (based on the number of email contacts you want to reach). It has a very easy to learn user interface. You can import your list of emails from a spreadsheet file easily. You can link to articles or content on any website (your own or others). You can include articles, images, coupons or other tidbits that your customers need or want.
Keeping your business name in front of your customers is smart. As they say, "out of sight, out of mind".
To find out more about Constant Contact, use this link: