What is HTML Mailer?
HTML mailer is the way an email templates is coded to include a format with both text and images. HTML mailer is usually created using an autoresponder that enables the creation of the html mailer without the needing to write any html code.
Marketers are using html mailer as they can create a designed email that is great-looking with lots of visual appeal. Instead of using plain black and white text emails, they use html mailers design to display a variety of colors, buttons, images, backgrounds, and fonts to convey their messages in a more impressive and many times more effective way.
Source: Morning Dough – HTML Mailer