What are custom tracking domains and why use them?

When you send a marketing email, every tracked link in it passes through a redirect domain before reaching its destination. By default, that redirect domain belongs to your ESP. So your carefully crafted email has links going through something like track.espname.com, a domain shared by thousands of other senders you've never met.

A custom tracking domain swaps that out for a subdomain you own, like click.yourbrand.com or go.yourbrand.com. The click tracking mechanism works exactly the same way. You're just routing it through your own branded infrastructure instead of your ESP's shared one.

How to set it up

1. Pick a subdomain (click.yourbrand.com, track.yourbrand.com, or go.yourbrand.com are all common choices)
2. Add a CNAME record in your DNS pointing that subdomain to your ESP's tracking server
3. Tell your ESP to use your custom domain in settings
4. Enable HTTPS (most ESPs handle the SSL certificate automatically, but double-check)

Most major ESPs support this. Mailchimp, Klaviyo, Twilio SendGrid, and Brevo all have custom tracking domain options in their settings, usually under domains or sending configuration.

Why it matters for deliverability

The biggest reason is reputation isolation. When you use your ESP's default tracking domain, your link domain reputation is tied to every other sender on that shared domain. If someone else on the same ESP runs a spammy campaign and gets their links flagged, your emails could suffer the blowback. With a custom tracking domain, your reputation is yours alone.

There's also a blocklist risk worth knowing about. If the ESP's shared tracking domain gets added to a blocklist, every sender using it takes the hit. Your custom domain won't be affected.

Security filters sometimes treat unfamiliar third-party tracking domains with more suspicion than established branded ones. A domain your recipients have seen in emails before tends to fare better than a generic ESP subdomain they've never encountered.

And from a trust angle, when a recipient hovers over a link and sees click.yourbrand.com instead of track.someesp.com, it looks a lot more intentional and legitimate. That matters especially if you're in a space where recipients are cautious about phishing.

One honest trade-off: if your own sending practices damage the custom domain's reputation, that's on you. You can't point to shared neighbors anymore. That's actually a good thing. It keeps you accountable and focused on sending to people who actually want your emails.

If you're not sure whether your current tracking setup is hurting your deliverability, our free email header analyzer can show you what's happening under the hood.