Best image formats for email signatures: Compatibility guide

2026-03-05

Using a professional image or logo in your email signature significantly boosts your brand's presence. However, the world of email rendering is notoriously complex, and not all image formats are created equal. Choosing the wrong file or embedding type can result in broken images, security warnings, or poor quality on your recipient's screen.

This guide will walk you through the formats you can rely on and the ones that are best left.

🔗Image formats that basically all email clients support

JPEG (.jpg or .jpeg): Best for photographs and complex images with many colors and gradients. Offers good compression for smaller file sizes.
PNG (.png): Ideal for logos, icons, and graphics needing transparent backgrounds. Supports millions of colors but can be of bigger file size than JPEG.

🔗Image formats that are widely supported, but come with a caveat

GIF (.gif): Perfect for simple animations or graphics. While widely supported and creating great visual effects, only use when required: Some email clients only show the first frame and not the animation, some may only show the animation after a user clicks on an overlay play button.

🔗Image formats you should avoid

SVG (.svg): While great for web, SVGs aren't supported in a growing number of email clients due to security concerns (cross-site scripting and others).
WebP (.webp), HEIF (.heif), AVIF (.avif), APNG (.apng), and others: Too new for most email clients and their integrated renderers. Some of these formats are not even yet supported by all browsers.
TIFF (.tiff), PSD (.psd): Avoid completely. These are high-quality, often uncompressed file formats intended for professional printing or editing, not for web or email display. Their file sizes are prohibitively large, guaranteeing slow loading and zero support from email clients.
BMP (.bmp): Avoid completely. A very old, uncompressed bitmap format primarily used by Windows. While being support by most clients, the file size is massive compared to an optimized JPEG or PNG for the same quality. Stick to the more modern standards.
MP4 (.mp4, .m4*) and other animation and video formats: Avoid completely. Email clients typically cannot play video files directly. Including them often triggers spam filters or results in a broken attachment icon. To share a video, use a static image that links to an external video hosting site.

🔗Linked image files

Linked images are great in theory, but often lead to problems in real life.

Due to security reasons, most email clients do not show linked images until the recipient allows their download. In the meantime, a placeholder image with an error message is usually shown instead.
You can not move the file on your web server.
Swapping to a new image may or may not be reflected in older emails, depending on the email client.
When the width or height of the image changes, it may have unwanted visual effects to your signatures.
After downloading the image, some email clients compress and resize the image, which may make it blurry. Some Outlook versions only do this when replying or forwarding an email with linked images.

All this neither creates a professional impression with the recipients of your emails, nor does it make the marketing department happy.

If possible, add images directly to your signature, not as linked images.

🔗Adding images directly

Images can be added directly, that means not as linked image file, as Base64 embedded image or as hidden attachment.

Hidden attachments, also known as inline attachments, are the long-term default. Virtually all email clients have always supported this format.
Base64 embedding is the more modern method. Instead of referring to a hidden attachment, the image becomes an integral part of the email's HTML code.

On the recipient side, email clients released after 2015 not only support hidden attachments but also embedded images.

On the sender side, support varies slightly depending on client and platform. But no need to worry: You do not have to think about it, your email client takes care of everything.
Let's take Outlook as example: All editions on all platforms support hidden attachments, the same is true for embedded images since 2016.

Set-OutlookSignatures and the Benefactor Circle add-on support both variants, allowing you to choose a preferred option while automatically mastering situations that require the use of a specific method.

🔗Conclusion and final advice

The golden rule for email signatures is compatibility over bleeding-edge technology. While new, high-efficiency image formats like WebP and AVIF are exciting for the web, the fragmented and rather traditional world of email is simply not ready for them yet.

To guarantee your professional signature renders perfectly every single time, rely on JPEG and PNG.

And remember: Embed, don't link! This keeps your images attached and visible from the moment the email arrives.

Following these simple guidelines will ensure your brand image is always presented flawlessly.