Gmail does not block your images, it steps in

by Francis Rozange | Sep 8, 2026 | Email Marketing

Abstract 3D render: an empty glass picture frame with one thin line of light beneath it

“Images are blocked by default.” That sentence is repeated in every email marketing guide, and it is true at one operator out of two.

At the other, something quite different happens, and it is more interesting.

Outlook blocks, and says so

Microsoft leaves no room for doubt:

“Blocking pictures can help protect your computer. Microsoft Outlook is configured by default to block automatic picture downloads from the Internet. You can, however, unblock pictures that you think are safe to download.”

The list of stated reasons contains one line that concerns you directly:

“Helping you avoid tracking pixels: invisible images that can tell a sender you’ve read the email.”

The tracking pixel is named in the justification for blocking. It is not a side effect: it is a stated objective.

Microsoft confirms it elsewhere, in a page about attack simulation: “Although you can configure Outlook to automatically download images, we don’t recommend it due to the security implications.”

Gmail does not block. Gmail steps in between.

Google took the opposite decision, and announced it in December 2013 on the official Gmail blog:

“Instead of serving images directly from their original external host servers, Gmail will now serve all images through Google’s own secure proxy servers.”

Its current help page confirms the default behaviour: “By default, when you get an email with an image, you’ll see the image automatically.”

Your images therefore display, without the recipient doing anything. But they are not served by you. They are fetched once by Google, analysed, cached, then distributed from its servers.

Google also writes that the analysis precedes reading: “Google scans images for signs of suspicious content before you receive them.”

One documented exception: “If Gmail thinks a sender or message is suspicious, you won’t see images automatically. Instead, you’ll be asked if you want to see the image.” Automatic display is a privilege, withdrawn at the first suspicion.

What the proxy breaks

The Google Workspace admin documentation is the most useful for understanding the practical consequences:

“Because of the image proxy, links to images that are dependent on internal IPs and sometimes cookies are broken.”

Three families of device stop working, and they are exactly the ones the market sells.

Cookie-personalised image content does not work: the proxy does not carry cookies.

IP-based geolocation on open does not work: the address your server sees is Google’s.

And the dynamic image, the one displaying a different countdown on each open, works once: the proxy caches, and then serves the copy.

At Apple the mechanics differ but the effect on measurement is the same: remote content is downloaded in the background whether the recipient opens or not.

Three environments, three fates for one image

Let us recap what becomes of an image placed in a campaign.

In classic Outlook: nothing displays until the recipient asks for it. Your message stands on the text, or it does not stand.

In Gmail: the image displays, served by Google, with no cookie, no real IP address, and cached.

In Apple Mail with protection on: the image is loaded systematically, through a relay, without that meaning anyone read it.

None of those three behaviours matches what a template designed for a browser assumes.

What to take from this for design

The oldest rule in the trade survives intact, and for a new reason: an email must remain understandable without its images.

That does not mean an email without images. It means the essential information, the offer and the expected action, must exist as text.

An email whose offer is written inside a single visual arrives empty at every Outlook recipient. The reader sees a grey frame and a link.

The alt attribute regains an importance it has been denied for years. It is not merely an accessibility accessory: at Outlook, it is the only content displayed in place of your visuals. An image without alt text is an empty space.

As for dynamic devices, the question to ask before paying for one is simple: what does a Gmail recipient see on the second open, and an Outlook recipient on the first?

What to do tomorrow morning

Take your last campaign and turn off image display in your mail client. Read what is left, without indulgence. If you cannot understand the offer, some of your recipients did not understand it either.

Then check your alt attributes, one by one. Not file names, not keywords: the sentence you would want displayed in place of the image.

If you use a countdown image, image personalisation or a geolocated map, test them on a Gmail address, twice, a few hours apart. You will immediately see what the cache does with them.

And stop relying on the pixel. Two of the three major operators neutralise it, each in its own way, and one of them writes it into the list of reasons it blocks your images.

Sources

LaFactory works email on the evidence: headers, DNS records, rejection logs. No open rate promises, ever. Get in touch for a deliverability audit.