Choosing images that work in every inbox

Most images display in every inbox without any thought. A few rules decide whether an image uploads at all, whether every reader sees it, and whether an animation keeps moving. Check them before you upload and you won’t have to come back.

What Letterhead accepts

• Any standard image file except SVG. JPEG, PNG, GIF, WebP, AVIF, HEIF (a common iPhone photo format), TIFF, BMP and ICO all upload. SVG files are rejected at upload, however you add them, because many email apps don’t show them and some block them for security reasons.
• Up to 10MB per file. A larger file won’t upload. Some accounts have a higher limit (for example, 20MB); if you regularly work with bigger files, ask your Letterhead contact whether yours does.
• The image itself, not a web page. If you paste a link to a web page, or a snippet of HTML, rather than an image file, the image block can’t use it. Save the image from the website to your computer, then upload that file.

Which formats display best

Accepted isn’t the same as reliable. From best to worst for email:

1. JPEG (JPG) is the best all-round choice: small files at good quality.
2. PNG is lossless and supports transparency, so it suits simple graphics and images with text. Files can be larger than JPEG.
3. GIF supports transparency and animation, so it suits short animations and simple graphics.
4. WebP, AVIF, HEIF or ICO upload, but fewer email apps show them than JPEG, PNG or GIF.
5. BMP and TIFF aren’t recommended. They make very large files, and TIFF is a print format.

Keep an animated GIF animated

An animated GIF stays animated when the file is under 1MB and you haven’t cropped or edited it in Letterhead. A larger GIF still uploads (up to your upload limit), but readers see it as a still image, and so does a GIF you crop or edit after uploading. To get a GIF under the limit, shorten the animation or reduce its dimensions in your own editing tool before you upload it.

Some accounts have a higher animated GIF limit, and on those a GIF stays animated up to that size instead. Bigger GIFs download in full every time a reader opens your newsletter, so they load more slowly.

If you send through Iterable, an image block can also show personalized images from data feeds instead of a file you upload.

Once you have the right file, see Adding and styling images to put it in your newsletter. If an image that meets all of these rules still won’t upload, or doesn’t show in the delivered email, contact support.