How do fallback versions work?

AMP emails use a multi-part MIME structure with three potential versions: text/plain (basic text), text/html (standard HTML), and text/x-amp-html (AMP content). Email clients that support AMP render the AMP version; all others automatically ignore the AMP part and display the next-best available format, typically the HTML version.

This fallback mechanism is automatic and invisible to recipients. A Gmail user might see interactive product carousels while an Outlook user sees static images of the same products-both experience a complete, functional email appropriate to their client's capabilities. The fallback isn't a degraded experience; it's an intentional alternative designed to achieve the same communication goals through traditional means.

Best practice requires designing the HTML fallback first, ensuring it delivers full value as a standalone email. Then layer AMP enhancements on top. Never treat the fallback as an afterthought-for most email programs, the majority of recipients will see it. Test both versions thoroughly and ensure calls-to-action and key content work in both. The AMP version is a premium experience for compatible clients; the HTML fallback is the baseline that everyone else sees-and \"everyone else\" is often most of your audience.