As an e-commerce company with more than 4 million subscribers to our daily fashion-sale alerts, we keep a close eye on what makes e-mails most effective.

We've sent more than 1.5 billion e-mails since starting our business five years ago and admit to our fair share of mistakes. We've gotten better, but along the way, we've learned a lot about what not to do.

Here are our top seven takeaways:

By Charlie Graham as seen in Inc.com