When should you use Images render at the right size?
email-image-rendering · functional · recommended
When should you use this check?
Run this on image-led campaigns, and on any template where the images were resized in the HTML rather than re-exported at the right dimensions. Declared dimensions that upscale or squash an asset make a careful send look careless, and the effect is worst on high-density screens, where a modestly upscaled image reads as visibly soft. It also catches a harder failure in the same pass: a source that resolves to something which is not image bytes at all, which renders as nothing.
When should you not?
Skip it on sends with no meaningful imagery, and on templates where every image is a spacer or a tracking pixel — the findings there are technically true and practically irrelevant. It is also not a judgement about file weight or load time, nor about whether the image is cropped by the client, which is the clipping check's question. If you only want to know whether assets resolve and come from approved hosts, the image-source check answers that at lower cost.
What does it inspect?
Every image in the email must load, and must be displayed at a size its file can actually fill. Stretching an image beyond its own pixels forces the mail client to invent the ones it does not have, which is what makes an image look soft or blocky — so an image displayed more than a quarter larger than its file is reported, as is one squashed or stretched out of its true shape. Good practice is to export at twice the display size and set the width attribute to half, so images stay sharp on the high-resolution screens most email is read on.
What does a failure mean?
A failure means an image's declared rendering size disagrees with its natural size beyond the allowed margin, or that the source did not resolve to image bytes. Upscaling is the common case and reads to a recipient as blur; squashing reads as distortion, and on a logo or a product shot it looks like a mistake rather than a compression artefact. The finding names the image, so it is directly actionable rather than a general complaint about the template.
What are the Standard defaults — and why?
One parameter carries the check: `maxUpscalePercent`, defaulting to `125` — a quarter over the asset's own size. The value is scale-invariant on purpose, because blur is a ratio rather than a pixel count, so one number judges a 16px icon and a 600px hero the same way. A quarter is chosen as the point where upscaling becomes visible on ordinary screens rather than only on high-density ones, which keeps the finding meaningful without failing every asset that is slightly off.
How does an agent call it?
{
"type": "email",
"validations": [
"email-image-rendering"
]
}
Who governs the Standard?
Schemafirst.org publishes community-governed standards for digital QA. ArbiterQA is a sponsor and commercial licensee of those standards; citation does not mean Schemafirst operates ArbiterQA.
Author ArbiterQA · Reviewed by ArbiterQA · 2026-08-14