Whenever an e-mail recipient opens your mail, they consciously or subconsciously deal with five issues until they're satisfied. These five issues will either induce the recipient to take the action you want them to take, or a lack of satisfaction may push them to the next e-mail. None of these five issues is easy to measure. None has objective factors that are easily influenced. But all are nonetheless key to converting click-throughs.
So what are the five critical issues that must be communicated to each recipient's perceptual reality
When someone receives your e-mail, they have certain expectations it will be relevant to what they've opted-in for. Your first goal is to show that relevance in the mailing. The greater the relevance, the greater the likelihood of click-throughs and the greater likelihood that future correspondence will be opened.
People must feel they can trust you before they'll click-through or buy from you. Design, content, layout and how relevant the content is convey trust. Design doesn't mean it must be pretty, but it must feel right. It must feel professional and easy to understand. This is one place where loyalty can buy a lot of wiggle room. People will put up with failures in other issues if they already trust you, but no one will deal with you if they feel they cannot trust you.
Value is in the eyes of the beholder. Every product or service has attributes. Value is how an individual assigns the benefits of each attribute to their needs. Have you listed all product attributes and articulated how they impact the recipient?
Privacy is closely related to trust! If you want a visitor's e-mail address or other personal information, you must realize they provide it as part of a value exchange. If you can acknowledge how you value their privacy and prove it through your actions it should help establish a solid relationship.
Security isn't about owning the most advanced encryption technology. Security is really about letting people know dealing with you is safe. It's about making sure recipients of you campaigns feel secure enough to click-through to your site.
Ultimately, confidence is the goal. Address all five issues. If they add up positively in visitors' minds, what they feel is confidence.