A custom tracking domain routes email click tracking through your own domain (links.yourdomain.com) instead of your ESP's shared tracking domain. Setup: add a CNAME record pointing your subdomain to your ESP's tracking endpoint. This takes 5 minutes and immediately removes your dependency on your ESP's shared tracking domain reputation. Every ESP supports this — it's the most underrated deliverability improvement you can make.
Custom Tracking Domains: Setup Guide and Why They Matter
The 5-Minute Fix Nobody Does
Custom tracking domains are the most impactful deliverability improvement that takes the least effort. Five minutes of DNS configuration. Immediate benefit.
Yet most businesses never set it up. It's part of a complete email infrastructure setup.
How Click Tracking Works
When your ESP sends an email with a link to yourdomain.com/product, it rewrites the link:
Without custom tracking domain:
https://click.sendgrid.net/ls/click?upn=abc123...
With custom tracking domain:
https://links.yourdomain.com/ls/click?upn=abc123...
Both redirect to the same destination. Both track the click. But the domain reputation is completely different.
Why This Matters
Spam filters evaluate every URL in your email. When a URL points to a shared tracking domain used by thousands of senders (including some spammers), the URL itself becomes a risk factor.
With a custom tracking domain:
- The URL points to YOUR domain (already trusted)
- No dependency on other senders' behavior
- Branded links look more professional to recipients
- Reduced chance of URL-based spam filtering
- Aligns with your subdomain strategy and DNS configuration
Setup by ESP
Klaviyo
- Settings → Domains → Custom Tracking Domain
- Add CNAME:
links.yourdomain.com CNAME trk.klaviyo.com
- Verify in Klaviyo
SendGrid
- Settings → Sender Authentication → Link Branding
- Add CNAMEs (SendGrid provides 2 records)
- Verify in SendGrid
Mailgun
- Domain Settings → Tracking → Custom Tracking Domain
- Add CNAME:
email.yourdomain.com CNAME mailgun.org
- Verify in Mailgun
ActiveCampaign
- Settings → Advanced → Custom Domain
- Add CNAME as directed
- Verify
Mailchimp
- Website → Domains → Email Domain Authentication
- Add CNAME record provided
- Verify
Choosing Your Subdomain
Common choices:
links.yourdomain.comemail.yourdomain.comclick.yourdomain.comgo.yourdomain.com
Avoid using email.yourdomain.com if your ESP already uses that for something else (some ESPs use it for DKIM). Check for conflicts before creating the record.
Practitioner note: I set up custom tracking domains for every client engagement. It's the fastest deliverability win available. One CNAME record, 5 minutes, immediate benefit. If you haven't done this yet, stop reading and do it now.
Practitioner note: Custom tracking domains also give your links a professional appearance. Recipients see
links.yourbrand.cominstead ofclick.sendgrid.net— better trust signals, better click rates. It's a deliverability AND marketing improvement.
If you want your email infrastructure fully optimized including tracking domains, authentication, and monitoring, schedule a consultation.
Sources
- SendGrid: Link Branding
- Klaviyo: Custom Tracking Domain
v1.0 · March 2026
Frequently Asked Questions
What is a tracking domain?
When you include links in email, your ESP rewrites them through a tracking domain to count clicks. By default, this is a shared domain owned by your ESP (e.g., click.sendgrid.net). All ESP customers share this domain. A custom tracking domain uses your own subdomain instead.
Why does the default tracking domain hurt deliverability?
The default shared tracking domain is used by every customer on your ESP. If another customer sends spam with links through that domain, the tracking domain reputation drops — and link reputation in YOUR emails suffers too. A custom tracking domain isolates you.
How do I set up a custom tracking domain?
1) Choose a subdomain (links.yourdomain.com or email.yourdomain.com). 2) In your ESP's settings, configure the custom tracking domain. 3) Add the CNAME DNS record your ESP provides. 4) Verify in your ESP. Takes 5 minutes plus DNS propagation.
Does every ESP support custom tracking domains?
Yes. Klaviyo, SendGrid, Mailgun, ActiveCampaign, Mailchimp, Postmark, HubSpot — all major ESPs support custom tracking domains. The specific CNAME setup varies by provider but the concept is the same.
Will changing my tracking domain break existing emails?
Links in already-sent emails will still use the old tracking domain and continue to work. Only new emails will use the new custom tracking domain. There's no risk in making the switch.
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