Why bother using plain text at all if HTML has so much more capability?
Depending on your recipients email client (Outlook) and the setting within it, they may have their security settings to not allow HTML. In this case they can only view your campaign as Plain text. When creating a campaign in Tellem you have the option to include Plain Text with your HTML version. If you create your campaign with the plain text included you will ensure that all of your recipients are able to view your message. Though, you will not have the tracking stats for the views of just the plain text version.