Keep it personal. You do not have the time to write an email to every person, but you want to give the reader the idea that you wrote this email personally for him or her. There are a lot of email and market automation programs where it is possible to personalise. Think of first name, last name, gender, etc. Besides that, A/B testing is becoming a trending topic. This allows you to send (slightly) different emails to your audience. You can change the content, subject, images, buttons or even the send date. The idea is that you change one of those aspects in one of the two mails you send. Those two mails go to a small part of your target audience. The E-mail that performs best, gets sent to the remaining target audience.