HTML email / HTML version
An HTML email is an email message built using HyperText Markup Language to create a visually formatted layout with styled text, images, colours, buttons, and structured columns, as opposed to a plain text email which contains only unformatted text. When you receive a marketing email with a logo, a banner image, branded colours, and a clickable button, you are looking at an HTML email. The HTML code defines the structure and appearance of the message, and the email client renders it visually for the recipient.
HTML email is the default format for marketing communications because it allows brands to present their identity consistently, use visual hierarchy to guide the reader’s attention, and include rich design elements that plain text cannot support. However, HTML email comes with technical complexity: different email clients render HTML differently, particularly Microsoft Outlook, which uses a version of Word’s rendering engine and requires specific coding techniques to display correctly. Most modern email marketing platforms provide template builders that generate HTML automatically.
The standard practice is to send a multipart email containing both an HTML version and a plain text version. Most email platforms send both simultaneously, and the recipient’s email client chooses which to display. Recipients who prefer plain text, or whose clients do not support HTML, see the plain text version. Having both versions also reduces the risk of certain spam filters penalising single-format messages, and ensures your email remains readable in every environment.
What is the difference between an HTML email and a plain text email?
A plain text email contains only unformatted text characters with no images, colours, layout, or links beyond the raw URL. An HTML email uses markup code to apply visual formatting: fonts, colours, images, columns, buttons, and spacing. HTML emails allow for richer, more branded designs and are the standard for marketing communications. Plain text emails are simpler, often perform better for personal-feeling sales outreach, and are required as a fallback for recipients whose clients do not render HTML.
Why does my HTML email look different in Outlook versus Gmail?
Outlook uses a version of Microsoft Word’s rendering engine to display HTML emails, which has significant limitations compared to web browser-based rendering. It does not support many modern CSS properties, handles fonts and spacing differently, and ignores certain layout techniques. Gmail and most other modern clients use browser-level rendering with much better CSS support. Designing email HTML for cross-client compatibility requires specific techniques: table-based layouts, inline styles, and Outlook-specific conditional comments.
Does HTML email affect deliverability?
The code quality of HTML emails can affect deliverability. Extremely large HTML files (above 102KB in Gmail) will be clipped. Emails with a very poor HTML-to-text ratio or that contain HTML formatting patterns commonly associated with spam may trigger filters. Broken HTML, such as unclosed tags or invalid markup, can cause rendering problems and in some cases trigger spam scoring. Using a clean, well-structured template and testing before sending are the most effective ways to ensure your HTML does not inadvertently affect deliverability.