MailChimp Inbox Inspector

At first glance, this seems like it might be an interesting option.

“Whenever you create an email campaign, do you spend hours testing it in all your different email programs and ISP accounts and spam filters? Or do you just click "send" and pray to the email gods? We feel your pain. That's why we created the MailChimp Inbox Inspector...”

http://www.mailchimp.com/add-ons/inboxinspector/