Time Each time you send an e-mail, you're taking up people's time. If you send e-mails too often, even the two or three seconds it takes to delete the message mailing list will be too much and they'll unsubscribe. Or if your e-mails are long-winded and wordy, sending them one a month could even be too much. Think about your readers and realize you're taking up their time - so you better offer them some good compensation.
Offers Speaking of compensation, while you should always be offering them quality content, use your e-mail list as a way to offer unique deals mailing list or coupons. This will act as an incentive not only for people to stay subscribed, but also to let others know that they too should sign up (and, of course, will hopefully boost your sales). Invest Don't use newsletters or e-mail campaigns as a way to make a quick buck. Instead, realize you're making a long-term investment in your customers.
Your list will grow more by creating life-long customers who are loyal to your business than by trying to hard sell everyone each time you send out an e-mail. Diversity Remember that each of your e-mails don't have to deal specifically with your mailing list business. Your e-mail list is a community, and it may be a great way for you to explore other topics and allow your readers to do the same.