HTML Email
HTML email uses markup to format a message with links, headings, images, and layouts. It can look plain or designed; rendering varies by email client.
HTML email uses HTML markup to format its message body. It can contain headings, styled links, images, and layouts. A short message with one formatted link can be HTML even when it looks like plain text.
Design for the receiving client
Email clients support different parts of HTML and CSS. A layout that works in a browser may lose styling or wrap differently in an inbox. Test the sent message in the clients and screen sizes your audience uses.
Keep essential information as text rather than baking it into an image. Add useful alternative text to informative images, use descriptive link labels, and check contrast. Microsoft explains how fonts, contrast, and image alt text support email accessibility.
A plain-text alternative gives clients another representation of the message. It should contain the same essential details and usable destinations for the main action and unsubscribe link.
Format and delivery
HTML is a format, not an inbox-placement guarantee. Authentication, sending history, recipient permission, and filtering still matter. Diagnose a delivery problem from message headers and provider reports before rebuilding a template on the assumption that HTML caused it.