If you use Google as your domain provider and want to set up custom tracking domain, please follow these steps.
Log in to your account (Instantly and Google Domain).
On Google Domain, navigate to My Domains and click Manage.
From the left-hand side menu, click DNS.
Click Manage Custom Records.
Click Create New Record.
Go to your Instantly Account Settings, and check the Use custom tracking domain.
Copy the data for the new record.
Paste the copied data.
Host Name: inst
Record type: CNAME
TTL: 3600
Data: prox.itrackly.com
Click Save.
On your Instantly account settings, under your tracking domain or subdomain, enter inst.yourdomain.com.(change it with your sending domain)
Click Check Status.
After SSL and CNAME records have been verified, click Save.