It’s true that your customers do want to hear from you. The fact you have a regular email marketing campaign is one of the magic elements boosting your ROI. But there’s such a thing as overkill. Once you come off a great campaign it’s tempting to run the same campaign again in an attempt to get the same results. The chances are you’re going to get diminishing returns.
Think as well about the kinds of metrics you're evaluating. You probably know that interaction with email campaigns is measured through open and click-through rates. While it's meaningful to review email response in this way, if this is all you measure, you're missing the bigger picture of the value of email to your company and its customers. These rich metrics in the email are great. However, there is a distinction must be made between:

For example, I can safely share that I listen to a lot of music, and I’m almost fanatic about sound quality. I might listen to an album with poor sound quality once, but I probably won’t go back to it. And to be clear, 95%+ of new recorded music has what I consider poor sound quality (due to an absurd standard of perceived loudness, which takes away natural dynamic range from the sound). That said, I’m not a hi-fidelity sound geek. I’m perfectly happy with my high-end studio monitors—I don’t buy $1,000 power cables, $5,000 CD-players, or $20,000 loudspeakers capable of playing back sounds too high for dogs to hear.
Great flexibility: Email marketing can work for every business. It doesn’t matter whether you sell houses, lingerie, or consulting; you can get lots of sales if you use the right email marketing strategy in the right place. And you can promote practically anything relating to your business—you aren’t limited to sending links to your sales pages. Or rather, if your emails are just links to sales pages, you’re doing it wrong.
This A/B test indicates that engagement is one problem, but your subject lines are an even bigger problem—and one you can solve right away. CTR rates are understandably lower among the less-engaged group, but you saw engagement increase with a punchier subject line, so there is room to improve CTR among cold leads. CTR rates are higher in the more engaged group, but with a better subject line, this rate could go through the roof.
Personas provide a multi-dimensional method of targeting. They’re based, as the name suggests, on a projected persona for each customer ‘type’. Get it right, and personas can help you enormously in both predicting behaviour and personalising your communications. Personas are a powerful technique, and they’re increasingly used to improve the usability and customer centricity of communications. 
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