You need to clearly know the target market you're emailing.
This is crucial if you have multiple different markets on your list.
I have one list of beginner entrepreneurs. People who are interested in starting an online business... but still learning the ropes of marketing, sales, and entrepreneurship. They might have a dayjob or be in college.
I have another list of 6-7 figure entrepreneurs. People who have established businesses and are looking to scale up. Who are full-time, have capital to invest in growth, and are looking for someone to help them in a certain area (like *cough cough* email marketing...)
Now... do you think the same email would apply to both markets?
But I would risk message dilution and being irrelevant. And when you're irrelevant... ain't no chance you're making sales.
So that's the first thing.
Know "Who" it is that you're targeting.
Create a "Dream Customer Profile" so you don't have to think about this every time you email.
Once you know exactly who you're emailing, you need to know...