Google is bringing AMP, its cut-down version of HTML, to email. Starting today, Gmail on the Web will be able to support embedded AMP content, with support rolling out to mobile clients later. Gmail will also be joined by Outlook.com, Yahoo Mail, and Mail.Ru, with their respective developers promising to add support soon.

AMP for email isn't just a warmed-over version of email with HTML formatting. The embedded AMP content will be able to offer features such as interactivity without having to click away from your inbox. For example, an online store could send you an email about a product or promotion you're likely to be interested in, and the AMP embed could allow scrolling through pictures of the products and even initiate the purchasing process. Or Pinterest could email you a selection of the day's popular items and you could pin them directly from your inbox.

Accelerated Mobile Pages were introduced by Google in 2015 as a narrow set of HTML, JavaScript, and CSS capabilities that produced pages that are fast to download and render, could easily be packaged together, and were amenable to being embedded in, for example, Google search results pages. JavaScript features were limited to those offered by a Google-supplied library. This greatly curtails the range of things that pages can do in favor of being extremely cache-friendly and having consistently good performance.

AMP was met with some resistance at its introduction. Web developers questioned Google's approach—its JavaScript library is used to define special tags rather than using conventional HTML—as well as the need for a specific, narrowly defined format to achieve good performance. Some of these concerns have been mediated by Google's plan to build AMP on Web standards and introduce a new governance model that ceded control to a pair of committees. Sitting on those committees would be representatives from across both the technology and the content publishing industries.

Those limitations are arguably what enable AMP's interactivity in email. It would be dangerous to support the browser's full, unrestricted range of JavaScript capabilities in an HTML email, but that same danger doesn't exist for an AMP email, because the JavaScript library is carefully controlled and limited. AMP emails can't perform arbitrary scripting; instead, they opt into certain prepackaged pieces of behavior that they want to use.