If you are using secondary domains for creating sending accounts, it's recommended to set up forwarding to your main domain (website). This way, when the clients enter your sending domain into a browser's address bar, they will be taken to your main website.
Log in to your Domains page and click on Manage
From the left hand menu, select Website
Click on Forward domain
Select Permanent redirect (301) for Redirect type.
Under Path Forwarding, select Do not forward.
In Forwarding over SSL, select SSL On - if you want redirect to work for both HTTP and HTTPS requests.
Confirm by clicking on Forward.
Learn more about scaling email outreach with secondary domains.