Don’t send a spam
This is the basic rule that should be respected, do not do it. Do not send email to anyone, if he did not allow. The chance that such a person will buy in your online store is very small.
The unsubscription button should always be visible. And it should be as simple as possible. Ideal also click on the link and you are logged out. Really makes no sense to hide the unsubscribe link.
Clear subject of the email
From e-mail subject should be clear what’s inside. People like surprises, but this does not concern mysterious emails with the subject “Featured” or “today only at an exceptional price”. The subject is something like the headline of your article.
Do not use Caps Lock
Neither the subject nor the body of the email, nowhere.
Speak a story
Email should not be merely a list of products at the moment to sell. Try to write a story.
If you know the names and surnames of your customers. Use them in the email.