Open Tracking, Click Tracking and Custom Tracking Domains: What They Do to Cold Email Deliverability

Every sequencer switches on open tracking and click tracking by default, and most cold emailers never question it. Both features work by changing what is inside your email: an invisible image for opens, rewritten links for clicks. Inbox providers see those changes. This guide covers what each one actually does, what it costs you in deliverability, and when a custom tracking domain is worth setting up.

How open tracking works

Your sequencer adds a tiny, invisible image to the bottom of every email. The image is unique to each recipient and is hosted on the sequencer's servers. When the recipient's mail app loads images, it requests that file, and the sequencer logs an open.

That means three things:

• Every tracked email contains an image. A plain one-to-one email from a real person almost never does. A remote image in an otherwise plain-text message is one of the patterns filters associate with bulk mail.
• Every tracked email is HTML. You cannot embed an image in a true plain-text email, so turning on open tracking quietly turns your plain-text email into an HTML one.
• The image is hosted on a shared domain unless you set up your own. Thousands of other senders, some of them spammers, load pixels from the same place.

Why open rates stopped meaning much

Even if tracking had no deliverability cost, the number it produces has become unreliable:

• Apple Mail Privacy Protection pre-loads images for many Apple Mail users when the message arrives, so an "open" can be logged for an email nobody read.
• Gmail and other providers proxy images through their own servers, which hides the reader's location and device.
• Corporate security tools often open and scan messages, and links inside them, before the recipient ever sees them. That shows up as opens, and sometimes as clicks, from people who did nothing.
• People who block images never register an open, even when they read and reply.

So open rate is inflated in some places and missing in others. It is fine as a rough "did this land at all" signal across a large send, but it is a poor way to judge a subject line, and a very poor reason to send a follow-up that says "saw you opened my email".

How click tracking works

Click tracking replaces every link in your email with a redirect link on the sequencer's tracking domain. When someone clicks, they hit the tracking domain first, the click is logged, and they are forwarded to the real page.

The problems are similar:

• The visible link and the real destination no longer match. Your email mentions acme.com, but the link points at a tracking domain. Mismatched links are a classic phishing signal.
• Shared tracking domains carry shared reputation. If other senders on the same domain send spam, filters can learn to distrust links on it, including yours.
• Security scanners click links to check them, so click data from corporate inboxes includes bots.

What a custom tracking domain changes

A custom tracking domain is a subdomain you own, such as track.getacme.com, pointed at your sequencer with a CNAME record. Most major sequencers let you set one per sending domain. The tracking image and redirect links then use your domain instead of the shared one.

What it fixes:

• Your links and images no longer share a reputation with every other customer of your sequencer.
• The link domain matches the sending domain, so the mismatch between sender and link mostly goes away.

What it does not fix:

• The email still contains an image and is still HTML.
• Open data is still distorted by privacy features and scanners.
• A bad list or a spammy message still hurts you. A tracking domain hides nothing.

If you are going to track, use a custom tracking domain. It is a single DNS record and it removes the worst part of the risk. Set it up on each sending domain, alongside the SPF, DKIM and DMARC records you already need.

Our recommendation by situation

Situation	Open tracking	Click tracking
First touch to a cold list	Off	Off, and no links at all
Follow-ups in the same thread	Off	Off
Testing a new domain or offer	On, with a custom tracking domain, for a short test	Off
Warm leads who asked for a link	Optional	On, with a custom tracking domain
Diagnosing a deliverability drop	Off. Use placement tests instead	Off

The pattern: the colder the recipient, the less you should add to the email. A first cold email should look like something a person typed: plain text, no images, no tracked links, ideally no links at all. Put the link in the reply once they are interested.

What to measure instead of opens

• Reply rate. The only metric that needs a human and cannot be faked by a privacy feature or a scanner. Track positive replies separately.
• Bounce rate. Keep it under 2%. See what a good bounce rate is.
• Inbox placement. Seed tests tell you directly whether you land in the inbox, the spam folder or the promotions tab. Run our free inbox placement test before a campaign and whenever replies drop.
• Replies per mailbox. If one inbox suddenly gets far fewer replies than its siblings on the same campaign, it is probably landing in spam. Rest it and check whether your emails are going to spam.

If you turn tracking off, what do you lose?

Less than you think. Most sequencers stop a sequence when someone replies, and that keeps working without tracking. You lose the ability to tell "opened but didn't reply" from "never saw it", but open data could not reliably tell you that anyway. Teams that switch off tracking usually find their reply rate is the number they were really watching.

The one real loss is A/B testing subject lines on opens. Test on replies instead. You need more volume per variant, so test fewer, bigger changes.

How to switch tracking off safely

1. Turn off open and click tracking in your sequencer's campaign settings. In most tools it is a per-campaign toggle, so check every active campaign.
2. Switch the email body to plain text if your sequencer offers it.
3. Remove links from first touches, including links in your signature. A signature with a logo image and three links undoes the work.
4. Keep a custom tracking domain configured on each sending domain anyway, for the campaigns where you do want click data.
5. Watch replies per mailbox for two weeks, not opens. That is your new baseline.

Tracking is one item on our cold email deliverability checklist. The rest of that list matters more, but this is one of the easiest wins on it.

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