Let’s see what an opt-in list is: a collection of e-mail addresses you take from people who are interested in your product, and want to join your autoresponder list. That means your autoresponder messages won't be considered spam, and the prestige of your business will help build user confidence and increase sales.
Now let’s talk about how to get one. There are many ways to collect addresses for your opt-in list, and you should set up as many as you can to develop a wide subscriber base.