It's not possible to know for certain if someone has read your email except in closed environments where that feature is supported. Read receipts are generally not supported for internet email. There are some tricks such as inserting a link to an image on your web server and if it loads you know the email was opened but many email programs block such things by default now. The closest match for what you are looking for is Good Mail who tries to make sure your emails get to inboxes and not spam folders :