The tone you adopt in your emails will be determined by the profile of your target audience. If they are 18-25 years olds and you’re selling music downloads, you won’t want to start your email with ‘Dear Jenny’. Similarly, if you’re selling holidays to the over-50s, you might not want to be too informal.
“You” is the best word you can use in a marketing email. It tells the reader that the email has been written for them, that it is addressing them.
Conclusion: Keep in mind that the online environment tends to be more informal than the offline world. So if in doubt, choose the side of informality but without becoming over-familiar.