Open/click tracking links default to a shared domain; a custom tracking domain (e.g. links.yourdomain.com) aligns tracking with your brand and protects you from shared-domain reputation swings. One CNAME record.
Why bother
Tracking links on a shared domain inherit every other user's reputation. A custom tracking domain isolates you and makes links look like yours — better for deliverability and click-through trust.
Setup
Settings → Domains → Tracking → Add. Choose a subdomain of your sending domain (links.company.io), add the CNAME turgo provides, and verify. SSL provisions automatically within minutes.
Assign to mailboxes
Assign the tracking domain per mailbox or per sending domain. All new sends use it immediately; historical links continue to resolve on the old domain.
Verification issues
A CNAME not resolving is almost always DNS propagation (wait up to an hour) or a proxied DNS entry (disable proxy/orange-cloud on that record if you're using Cloudflare).