Many retailers, travel marketers and B2B marketers send offers only to their best buyers. Often, however, the recipient doesn’t know how special they are, because it’s not mentioned in the email that this is truly an exclusive offer.

If you are segmenting based on buyer status, and offering special incentives as a result, take credit! Let your VIP customers know they are special, and that you've sent them these great offers because they are valued customers.

American Express positions itself as a partner to the small businesses that carry its business gold and platinum cards. Recently, the company offered a high-profile promotion opportunity to a select list of business cardholders-- and the email clearly notes why they were selected. The email also follows the best practice of asking for feedback at the bottom: "Tell us why you would or would not consider this opportunity."

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Conclusion: It's relatively easy to get customers to subscribe to your newsletter, but it's hard to keep them subscribed. Making your content relevant from the earliest moment in your email relationship -- registration -- is one way of keeping those customers around.