What is the key to relevance in email? Simple… it is knowing what the customer is interested in.
Whilst not wishing to be too prosaic, email marketing is the pursuit of relevance. Relevant emails get read and make money; irrelevant emails go into junk or worse still get unsubscribed (leading to a subsequent loss of lifetime value).
The art of good email is knowing what someone is interested in, and that applying this to all future email communications.