Most marketing email contains an invisible 1×1 image that reports back when you open the message. Loading it tells the sender the time you opened it, roughly where you were, and what device you used — repeatedly, every time you re-open. One setting stops nearly all of it: tell your mail client not to load remote images automatically. That's the whole fix.
How the pixel works
An email is HTML. When your client renders it, any image with a remote URL is fetched from the sender's server. That request is a visit, and it carries the usual details a web request carries.
The tracking image is a transparent one-pixel file with a unique URL per recipient. So the fetch says: this specific person, at this time, from roughly this location, on this device, opened the message. Nothing about it is technically exotic — it's an ordinary image request being used as a beacon.
Tracked links
The second mechanism. Links in marketing email usually point at a redirect on the sender's domain, which records the click before forwarding you to the real destination. That's why the URL in a marketing email rarely matches where you end up.
What it reveals
| They learn | How |
|---|---|
| That you opened it, and when | The pixel request |
| How many times you re-opened it | Repeated requests |
| Approximate location | IP address on the request |
| Device and mail client | User-agent |
| Which links interested you | Redirect tracking |
| That the address is live and read by a human | Any of the above |
That last row is the one that matters beyond privacy. An address showing engagement is worth more than a dormant one, so it gets promoted into better lists and resold at a higher price. This is the concrete reason not to open, and especially not to click, mail from senders you don't recognise — the same logic that applies to unsubscribe links.
How to block it
Turn off automatic remote images
The single setting that does most of the work:
- Gmail: Settings → General → Images → "Ask before displaying external images".
- Outlook: Trust Center → Automatic Download → block automatic download of pictures.
- Apple Mail: Privacy Protection → turn off "Load remote content in messages" (Apple's Mail Privacy Protection also proxies image loads, which breaks the signal in a different way).
- Proton Mail: Settings → Messages → block remote content by default.
You'll see broken layouts in some marketing mail, with a "show images" prompt. That prompt is the point: loading becomes a decision rather than a default.
Use a service that strips trackers
DuckDuckGo Email Protection and Firefox Relay both remove common email trackers from mail they forward, before it reaches you. That's a genuine feature and it happens without you configuring anything. Per each provider's documentation. Checked: 2026-08-19.
Worth saying plainly: Don't SPAM Me does not do this. We forward mail without stripping trackers. If tracker removal is what you're after, those two do it and we don't. The comparison.
What blocking images doesn't do
- It doesn't stop the mail arriving, or reduce how many companies hold your address.
- It doesn't cover tracked links — those only fire when you click, so the defence there is not clicking.
- Some clients pre-fetch images through a proxy, which protects your IP but may still register an open.
- Plain-text-only mail has nothing to block, and transactional mail often tracks too.
Where it sits in the bigger picture
Tracker blocking controls what a sender learns about you after they've reached your inbox. It's worth doing, it takes one setting, and it's genuinely separate from the question of who can reach you at all.
That second question is the address-level one. The complete guide to email privacy covers both halves.