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HTML Limitations in Email
HTML Limitations in Email

Learn about the limitations of using custom HTML in your email newsletters and automations.

Written by Peter Connolly
Updated over a week ago

While SmartrMail allows you to add custom HTML blocks when composing your email newsletters and automations, it's important to remember that while the majority of email content will display in your web browser, not all HTML content is supported by email inboxes.

In particular, the following types of HTML code are not supported by email inboxes and should not be used when composing your emails:

  • JavaScript

  • Flash

  • Embedded audio

  • Embedded video

  • Forms

  • <div> layering

  • <iframe>

Additionally, the following types of HTML code are not universally supported by email inboxes:

  • Background images

  • Custom web fonts

  • Embedded CSS

  • Image maps

  • Wide layouts

While your emails may appear fine in your inbox, they may not be rendered properly for your subscribers in their inboxes and so should be used with caution. To be on the safe side, avoid using these types of HTML code as well.

Common Workarounds

Below are some common workarounds that we suggest in place of unsupported HTML content.


JavaScript is a programming language that makes web content interactive. It's common in websites, but the vast majority of email clients do not support it.

Instead use an animated GIF to make your content more engaging.

Iframe Elements

An <iframe> (inline frame) is an HTML element that embeds content from one website into another. Inline frames are often used to insert content from another site like video, audio, or forms into another website with minimal code. The vast majority of email clients do not support iframe

Instead, link to the content you want to display in your campaign.


Flash displays animations and graphics on websites, but most email clients block it.

Instead use an animated GIF to make your content more engaging.

HTML Forms

Text fields, text inputs, radio buttons, and checkboxes are simple HTML form elements. Some email clients will display forms, but unfortunately, subscribers won't be able to submit them.

Instead, link to a Google Form or a form on your site.

Embedded media

Autoplay and click-to-play media won't play in an inbox unless your subscriber's email client supports HTML5 <video> and <audio> tags. Only one major email client, Apple Mail, supports these tags, so it's best to avoid embedded media and consider an alternative.

Instead link an animated GIF in your email to the video content

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