Email Tracking Pixels: What They Are and How to Block Them

Open a marketing email and there’s a good chance you’ve just told the sender that you opened it, when, on what device, and roughly where you were. You didn’t click anything. You didn’t reply. You just looked at it.

The mechanism behind this is the tracking pixel, and it’s in far more of your mail than you’d guess. Not just newsletters: sales tools, recruiters, PR outreach and “did they read it?” plugins all use the same trick.

How a tracking pixel works

A tracking pixel is a tiny image embedded in the HTML of an email, usually 1×1 pixel and transparent, so you never see it. Crucially, it isn’t attached to the message. It’s hosted on the sender’s server, at a URL that’s unique to you: something like track.example.com/open/a8f3c91d.gif, where that ID maps to your address in their database.

When your email client renders the message, it fetches that image over HTTP. That single request tells the sender’s server:

• That you opened the email, because the unique URL was requested at all
• When you opened it, from the request timestamp, including every re-open
• Your IP address, which gives a rough location
• Your device and mail client, from the User-Agent header

None of this needs your consent or a click. Rendering the email is enough. It’s how a salesperson knows to ring you twenty minutes after you read their cold email, and how a marketing platform scores you as a “warm” lead.

How common is this?

Endemic is the honest answer. When the BBC asked the makers of the Hey email service to analyse their traffic in 2021, about two-thirds of emails sent to personal accounts contained a tracking pixel, and that was after excluding spam.

Academic work backs this up. Princeton researchers studied nearly a million emails in I never signed up for this! Privacy implications of email tracking and found that 70% contained resources flagged as trackers, and around 30% leaked the recipient’s email address to a third party when opened. That last part is worse than a simple open receipt: it lets data brokers connect your inbox activity to the profile they’ve built from your web browsing.

What the big providers already do (and don’t)

The major providers have all responded to this, but in different ways, and none of them fully closes the hole.

Apple Mail has shipped Mail Privacy Protection since iOS 15 and macOS Monterey. With “Protect Mail Activity” on, Apple downloads remote content in the background through proxy servers, before you ever open the message. Your IP is hidden and every email looks “opened”, so the sender’s open data becomes useless. It’s clever, but note the approach: the pixels still fire, they just fire with junk data.

Gmail has loaded images through Google’s proxy servers by default since 2013. That hides your IP address and location, which is genuinely useful. But the proxy still fetches the pixel when you open the message, so the sender still learns that you opened it and when. Open tracking works fine against a default Gmail setup.

Outlook is a mixed bag. Classic desktop Outlook blocks automatic picture downloads from unknown senders by default, which does stop pixels. Outlook on the web and the new Outlook tend to load images through Microsoft’s service instead, which hides your IP but, like Gmail, still confirms the open.

The reliable fix: don’t load remote images

Every tracking pixel depends on one thing, which is your client automatically fetching remote content. If the image is never requested, the sender gets nothing. No open, no timestamp, no IP, no device fingerprint.

The trade-off is that legitimate images don’t load either, so newsletters arrive looking bare until you choose to display them. In practice that’s a good default: most email is perfectly readable as text, and you can load images on the handful of messages where they matter.

Here’s where the setting lives in each client:

• Gmail: Settings → See all settings → General → Images → “Ask before displaying external images” (Google’s instructions)
• Apple Mail (Mac): Mail → Settings → Privacy → turn off “Protect Mail Activity”, then tick “Hide IP Address” and “Block All Remote Content”. Or leave Protect Mail Activity on if you prefer Apple’s proxy approach
• Apple Mail (iPhone/iPad): Settings → Mail → Privacy Protection
• Classic Outlook: File → Options → Trust Center → Trust Center Settings → Automatic Download, and keep “Don’t download pictures automatically” ticked (Microsoft’s guide)
• Thunderbird, Evolution, KMail and friends: the desktop Linux clients block remote content by default and offer a per-message “show remote content” prompt, which is one of the quieter arguments for them. Our Linux client roundup covers where each one puts the setting

Or use a client where this is the default

Toggles work, but they’re scattered across apps and easy to get wrong on one device out of four. The alternative is a client that treats remote content as hostile until you say otherwise.

That’s how Kanmail handles it: remote images are blocked on every account by default, and you load them per message when you actually want them. Because it talks IMAP directly to your provider, there’s no middleman server reading your mail either. There’s more detail on both in the privacy and data and security docs.

Why bother?

It’s tempting to shrug at a newsletter knowing you opened it. But the same pixels sit in cold sales outreach, in emails from a landlord or a lawyer, in messages from anyone you’re negotiating with. “They read it Tuesday at 9:14 and again at lunch” is leverage, and by default you’re handing it over every time you open a message.

Blocking remote images is the rare privacy measure that’s genuinely easy. Flip the setting, or use a client that ships with it flipped, and opening your email goes back to being nobody’s business but yours.