A few words to the wise on your opt-in emails, or newsletter.
1. Use double opt-in
If you are using a single opt-in, it is very possible to end up with someone being added to your newsletter and yet deleted in a subsequent confirmation email sent out that they didn't request.
Double opt-in is a proven way of preventing this from happening. It basically works like this, your auto-responder will send out a confirmation email to the address you have on file that the user provided to you.
This email should have an image attached stating that the user should respond to the email by typing "yes" to receiving your newsletter. If they do so, they are added to your newsletter list and you can then send out future newsletters to them. If however, they do not respond to this email you will have a duplicate and a confused subscriber.
2. Don't over-mail!
One of the most popular email campaigns out there is those using mass emails. These often fail to get added to a subscriber's mailbox in the first place. If you send out a daily or weekly email, the chances of someone opting out is quite high! Keep your emails focused on the products you offer to your list. Don't over-mail them. Keep your campaigns to only 1 or 2 products on sale per campaign. A newsletter has less chance of being over-mailed than a monthly sale or sale offer.
The best method is to use your newsletter as an exit to the sales funnel of your business. This is the funnel where you offer a product or service to someone that just purchased from you. You should have a good balance of providing useful information and sales-related content.
A few months ago I heard a customer that was trying to figure out how to make money online. In her search for information, she ended up subscribing to a couple of newsletters online and reading the emails. Then one day she decides to cancel her subscription but can't find the email that she subscribed to.
So she goes to her main email in her autoresponder account and finds that she has been unsubscribed to 3 different newsletters.
She decides to call her autoresponder to find out why, but can't find the response. She tries to contact the companies email, but to no avail. She contacts the customer service line and finds that the newsletters she unsubscribed from are actually not her newsletter but a partner's newsletter that she subscribed to.
This is a great way to gain insight into a customer's needs and wants. You can use that information to create more profitable campaigns that reach further along the sales funnel.