Why do I receive both a TEXT and HTML version of my email?

Email is delivered in a Multi-part MIME format, meaning email messages are sent as an HTML with a text back-up version. When sending a test email you will receive a copy of both the Text and HTML version of your email. When you launch your email, however, recipients will only receive one version of your email. Most recipients will receive the HTML version, those few who are unable to will receive the Text back-up version