Custom tracking domain

One CNAME so tracked links carry your domain instead of ours. Set up in the dashboard.

When a broadcast has open or click tracking on, the pixel and the links in it point at a host we run. Without a tracking domain of your own that host is a shared emails.sh address, which means the links in your mail are visibly somebody else's. A custom tracking domain replaces it with a name under your own domain.

PATCH /v1/domains/:id is the same thing in one field: {"tracking_host": "click.mail.acme.com"} sets it and {"tracking_host": null} clears it, with the same live CNAME check and the same refusals. Use whichever fits the code you are writing. A bare label is expanded under the domain, so "click" on mail.acme.com means click.mail.acme.com. open_tracking and click_tracking are not settings here and a body carrying either is refused by name with 422 tracking_switch_not_supported.

The record#

One CNAME. The host has to sit under a custom sending domain you have already verified, which is what keeps somebody from pointing a tracking host at a domain they do not control. click.<your domain> is the suggested name and the one most people use.

# Check it resolves before you rely on it
dig CNAME click.mail.acme.com +short
# expect: track.emails.sh.

What the links become#

Two URL shapes get rewritten, and both take the tracking host as their base. The open pixel is /o/<message id>.gif and a tracked link is /c/<link id>.

Without a tracking domain:
  https://emails.sh/o/f3a91c07-4e28-4b6d-9c15-8d02a7e5b431.gif
  https://emails.sh/c/7d2e9a10

With click.mail.acme.com pointed at track.emails.sh:
  https://click.mail.acme.com/o/f3a91c07-4e28-4b6d-9c15-8d02a7e5b431.gif
  https://click.mail.acme.com/c/7d2e9a10

Why bother#

The links look like yours

A recipient hovering a link in your newsletter sees your domain. On a shared host they see ours, which is the sort of thing that makes a careful person not click.

Reputation is yours

A shared tracking host carries everybody's links, and a link scanner that has seen something bad on it has seen it on the same hostname as yours.

It survives a move

The CNAME is yours. Pointing it somewhere else later is a DNS change rather than a rewrite of every link already sitting in an inbox.

Tracking is off by default#

Nothing is tracked unless you ask for it. On a broadcast that is track_opens and track_clicks, both defaulting to off. A transactional send through POST /v1/emails is not tracked and has no pixel in it.

Leave it off for transactional mail. A receipt does not need a pixel, and an invisible image in a password reset is the kind of thing that gets a message filed as suspicious by a scanner that has no way to tell your pixel from anybody else's.

One link is never rewritten under any setting: the one-click unsubscribe. Putting a redirect in front of it breaks RFC 8058, which is the rule Gmail and Yahoo cite in their bulk sender requirements. See /docs/topics.