Most modern email clients send HTML emails by default. For example, Gmail and Yahoo Mail have built-in WYSIWYG editors that you can use to write HTML messages. However, if you want to write HTML in a third-party editor and then use it in your email client, it can be a bit tricky. Learn how to create and embed HTML in Gmail, macOS Mail, and Thunderbird.

Gmail and the Mail app on a Mac do not offer a way to compose an HTML email within the client. However, you can send an HTML message through either of these clients by copying and pasting HTML code created in another application.

Write your email in an HTML editor. Make sure to use full paths, including URLs to external files.

Once the HTML file is complete, save it to your hard drive (it doesn't matter where).