In the book entitled:
Permission Marketing: Turning Strangers into Friends and Friends into Customers
Seth Godin carefully explains his concept of getting customers to buy-in to receiving more communication from you. What I like about Godin’s approach is he realizes that business transactions are basically just a relationship between two people, at some level. Therefore, principles at work in personal relationships can also be applied to the business arena.
The books has been around for a while but is worth reading. I don’t know of any source that explains permission marketing better.
When building your email campaign or strategy, don’t get so bogged down with the technical details that you lose sight of the relationship aspect.
This book has had a profound impact on how I think about marketing, and I believe it will have the same impact on you.