HTML email
An email rendered with HTML and CSS — supports images, structured layout, and styled buttons. Plain text is the alternative.
HTML email is email rendered using HTML and CSS, allowing for images, structured layouts, styled buttons, and visual branding. It's the dominant format for marketing email. The alternative is plain text — no formatting, no images, just words.
HTML email rendering is notoriously inconsistent across clients. Gmail strips certain CSS, Outlook (especially Outlook desktop) uses an antiquated rendering engine that doesn't support flexbox or grid, and various mobile clients have their own quirks. Most production email programs use frameworks like MJML or rely on email-development services like Litmus and Email on Acid for client testing.
Plain-text email has a different niche: it's the format for cold outreach, founder-to-founder communication, and any email that should look like it came from a person rather than a marketing department. Plain text often outperforms HTML on engagement for low-volume, high-relevance sends because it looks more personal — but for branded campaign sends, HTML is essential.