One barrier that many small companies have to confront when they consider starting a newsletter -or any other e-mail based strategy- is the lack of a good recipients' list. "We have few customers" or "We don't have the e-mail addresses of our customers" are the main concerns they usually have.
Well, the fact that you don't have any e-mails is a problem. In fact it is a catch 22 problem: you don't start a mail strategy because you don't have a good list, and you don't maintain a good list because you are not using e-mail at all.
However, e-mail customer relationship, marketing, or customer retention need long-term strategies. So, the fact is that, if you don't start building your list right now you'll never have a list at all.
There are a lot of ways to proactively start growing a good e-mail list, and buying a database is not among them (they are very inaccurate and, in most cases, even illegal).
Ways to grow your list
Try to maintain a good (I mean: with a lot of added value) newsletter and promote it as hard as you can: in envelopes, business cards, brochures... and ask people to sign in or send you their e-mail in order for you to subscribe them.
Slowly but surely, make e-mail your main and natural way to communicate with customers. Just not use it for marketing or newsletters. Start sending your invoices by e-mail. Notify your customers by e-mail about product availability, order confirmations, product deliveries, and so on. This way they'll get used to receive e-mail from you, and will be more receptive to your information through this means.
Get as many e-mails as you can from your current customers. You can ask for their e-mails when you talk to them on the phone or in commercial visits. Ask for it in your paper-based communications too (ex.: invoices).
Ask for their e-mail to the visits that get into your facilities. For example, if you have a shop, inform the visitors about the existence of your newsletter or the value-added services you can offer them by e-mail (ex: product availability notifications, catalog updates...).
Of course, put a subscription box to your newsletter on your website. Make it easy to subscribe (but comply with law offering double opt-in, more on this on next posts). If you make it even easier to unsubscribe in case they don't want to keep receiving your mail, the will be less wary about subscribing in the first place.
Another fantastic way of getting a lot of e-mails at once is by arranging a contest or competition. A good place to start is in business events or conventions. If you have a stand there, collect names and e-mails from visitors and offer several prizes. They not have to be very costly, and can be your own products. Notify the visitors that they e-mails are going to be used only to send them your newsletter and that is very easy to unsubscribe if they're not interested later. You can arrange this kind of competitions in your shop or in your website. They are an effective way to grow your list of people interested in your products or services.
Once you start your strategy in a sustainable way your list will grow fast.