Email tracking in Gmail: how it works and what you can trust

Gmail doesn't tell you whether someone opened your email. To find out, you need something extra, and most of what's sold for this is heavier than it needs to be. Here's how tracking actually works, the simple ways to add it, and how far I'd trust the numbers.

How open tracking works

A tracked email carries a tiny invisible image with an address unique to that email. When the mail program loads the image, the tracking server notes the request and records an "open". That's the whole trick, and it explains every weakness below: the server knows an image was fetched, not that a person read anything.

How click tracking works

Each link in the email is swapped for a link through a tracking address, which notes the click and forwards the reader to the real page. It's more reliable than open tracking because someone or something had to request that link, although security filters at some companies follow links automatically to check them, which can record clicks nobody made.

Three simple ways to track in Gmail

1. Read receipts

Read receipts are built in and need no extension, but only work and school accounts have them, not personal @gmail.com addresses. An admin has to allow them, the recipient may have to approve each one, and Google itself says not to rely on them. They only suit internal or friendly email.

2. A browser extension

A small extension adds the image and link tracking when you send from Gmail. It's fine for tracking a few personal emails. Before you install one, check what it asks to read: many want access to your whole mailbox. It also only works from the browser it's installed in.

3. A sending tool

If you send to a list rather than one person, tracking belongs in your sending tool. You connect the mailbox, the emails still go out from your Gmail address, and nothing needs installing in the browser. mailzy works this way: its analytics show sends, replies, opens and clicks per campaign and per step, and you can switch open and click tracking off for any campaign.

Can you track Gmail without an extension?

Yes, but only in a limited way. Read receipts need a work or school account. A hosted tracking image can be pasted into each email by hand, which works for one message and not for a list. For anything regular, a sending tool is the route with nothing to install.

Why open numbers are unreliable

• Apple Mail opens things by itself. With Mail Privacy Protection on, Apple downloads remote images in the background when the email arrives, not when it's read. An "open" can appear seconds after delivery from someone who never saw it.
• Gmail fetches images through its own servers. Google's image proxy stands between you and the reader, so you don't see their real location or device, and repeat opens can go uncounted.
• Images can be blocked. If a mail program doesn't load images, a real reader never registers.

So opens can be too high and too low at once. mailzy counts Apple's automatic opens apart from real ones for this reason, but no tool can make the number exact.

Does tracking hurt deliverability?

It can. A tracking image and rewritten links are extra things for a filter to look at, and a shared tracking address carries the reputation of everyone else using it. My advice for cold email: keep the first email short and plain, and if you track clicks, do it through a tracking domain of your own instead of a shared one.

What I'd actually watch

I judge cold email by replies. A reply can't be faked by a robot, and it's the only number that turns into a meeting. Use opens as a rough signal: a big drop across a whole campaign can point to a deliverability problem, but it isn't proof. The sure way to know where you land is an inbox placement test, which sends to real test mailboxes and reports where the email ended up.

More on this in what a good open rate really tells you.