These limitations apply to classic Outlook for Windows, the original Outlook desktop app. Microsoft’s new Outlook for Windows displays emails differently, so most of these limitations don’t apply to it.

Learn more about the two versions in Microsoft’s Feature comparison between new Outlook and classic Outlook.

Web fonts, such as Google fonts, are not supported. Therefore, you must include an email-safe fallback font.

Classic Outlook for Windows can behave unpredictably when using non-email-safe fonts. For example, text can default to Times New Roman even when you include a fallback font in the CSS. To prevent this, add Outlook-specific styles to the head of your campaign’s HTML code.

Learn more in Add web font in EasyEditor.

Forwarding emails from classic Outlook for Windows can cause the appearance of the email to change. As soon as the email is forwarded, Outlook rewrites the HTML and CSS code, which can cause unwanted issues such as gaps, misalignment and changes to line height. It also causes any blocks which have been set to display only on mobile to also display on desktop.

Unfortunately there is nothing that can be done to prevent this happening, as we have no control over the code at the point of forwarding. We'd recommend avoiding using blocks that display only on mobile if you are aware that your contacts forward emails from classic Outlook for Windows.

Background images don't display in classic Outlook for Windows. Therefore, you must include a fallback background colour for displays where the image does not load.

When using background images in email design, it's best to reserve them for simple textures or patterns that won't matter if they're not visible. Never add background images that include text or essential visual information as it might get lost.

Many CSS techniques used in modern web design, such as overlapping content or rounded corners, are not supported by classic Outlook for Windows.

You can still use these techniques in email design, but it's essential to test on classic Outlook for Windows to ensure that your design still looks great when CSS is not supported.

Interactive email content uses code not currently supported by classic Outlook for Windows. Therefore, you must create static fallback content.

If you have many contacts opening your campaigns in classic Outlook for Windows, you should focus on other ways to make your content more engaging.

Learn more in our blog 5 best practice tips for email marketing.

Animated GIFs are now widely supported in Outlook on Windows. However, older versions of Outlook might display only the first frame or loop the animation a few times.

Therefore, it's essential to make sure the first frame of the GIF contains any vital content in case the animation does not play.