Have you ever thought about changing the pre-header (the very tippy-top portion of your email campaigns) in your email templates to something more compelling?
For example, the default pre-header in MailChimp is a link to view the email in your browser:
Here’s a pre-header that asks recipients to “add us to your address book:”
Nothing wrong with all the above, but some of you might want to try inserting a compelling offer up there instead, like this one from Banana Republic: