The ideal type of opinion (unrelated to your expertise) is one that doesn’t offend anyone, but makes some people relate to you more. For example, I’m a vegetarian. I used to protest whenever there wasn’t a big piece of meat on my plate. But when I tried eating just veggies for a couple of months, I realized I felt a lot more energetic. Sure, it’s more ecological. And often animals are treated cruelly. But those aren’t the things I emphasize if someone asks why I’m a vegetarian. No one in their right mind has a strong negative reaction to someone eating food that makes them feel energetic, right? But for some vegetarians it’s a very meaningful choice, so it might have a positive impact on those people. That said, I highly doubt that my choice of diet have any direct impact on my sales.
Genuinely effective campaigns segment the market as carefully as possible, and target accordingly. Relevancy is key for getting people to open emails and respond to your CTA – but what's ‘relevant' differs from person to person. If you're going to make your emails as relevant as possible to everyone who reads them, you need to Segment, Target, and Position.
When you're using email as a marketing tool, you're working on a pretty personal basis. This isn't ‘drive-by' stuff -you're directly targeting customers from their inboxes. There's a huge amount of potential which comes with this kind of marketing... but you'll only reap that potential if you REALLY understand both the marketplace you're operating from, and the audience you're talking to.
Don’t talk down to people. I think this should be obvious. But looking at the email offers I get, clearly it isn’t. Don’t tell people, “Not buying this product would be idiotic!” or “Only a fool doesn’t understand the value in this service.” This whole email marketing strategy relies on you making people understand the value they can get from you. And sometimes that means making people see the downsides of not buying. But you can do that in a friendly, respectful way.