How to Create HTML-Based Email in Yahoo. Yahoo Mail supports both plain text and rich text (HTML) email composition. There are benefits and detriments for each method, but if you want to use ...

You can create HTML-based email templates within Salesforce to use for your business. The HTML email form can be used to create a custom signature that includes an image.

And they correctly note that this problem could make advanced HTML email trickier for marketers and other people who need or like to use HTML email.