What is an HTML email?
HTML Mail sends the entire mail message with rich HTML formatting. This is a technology frequently used to send professional marketing newsletters, party invitations and special occasion greetings.
Most but not all email clients support HTML mail. Although result may differ with different formatting, HTML Mail has been tested to render relatively well with mail clients such as Mail on iPhone and iPad, MS Outlook, Android, Thunderbird and Mail on Mac.
Known clients that sometimes struggle with HTML mails include the web version of Gmail and the web version of Yahoo! Mail.