When should you use Email still legible with images off?

Run this on image-led campaigns and on any first send to a new audience. Images blocked is what Outlook shows every recipient who has not added you to Safe Senders, so this is not an edge case — it is the default experience for a meaningful share of business inboxes on the send that matters most. It asks the harder question alt text alone cannot: with images off, does the email still say what it is offering and give the reader a way to act?

Skip it on text-led mail that barely uses imagery, where the answer is obviously yes and the check spends budget confirming it. It is also not a substitute for the alt-text check — that one finds missing and useless alt values across every image cheaply, while this one judges the resulting experience as a whole. If you have not yet fixed known alt-text failures, run that check first: this one will simply tell you the consequence of them.

an email that says nothing with images blocked; an offer that exists only inside an image; no route to act when images do not load

A failure means that with images blocked, the message does not communicate its offer or does not present a usable way to act on it. That is the strongest form of image-dependency finding, because it does not depend on any single asset being broken — the email is working exactly as built and still saying nothing. The recipients affected are precisely the ones least familiar with you, since they are the ones who have not yet marked you as safe.

This check has no tunable thresholds. It is a judgement about what the message says with images blocked — the text and alt text an images-off reader receives, read from the message source — and there is no numeric limit or configurable list that would meaningfully calibrate "does this still communicate"; the answer is holistic by nature. It renders nothing, so there is no client or width to choose either: what an images-off reader receives is the same everywhere.

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