You can redirect domains to your main domain using the Redirect Domain Tool.
To redirect another domain to your website, follow these steps:
Go to your website Dashboard.
On the side menu, click Settings
Click on Change Domain and select Add Existing Domain
Enter the domain you want to redirect to your main domain (including www).
You will get a message that the domain was added successfully to your domain list, then click Save
Next, click the arrow button next to Change Domain, and select Redirect Domains from the drop-down menu.
Click the Redirect Existing Domain button.
Enter the domain (including www) and click Save
Make sure that the domain that redirects to your main domain on SITE123 is set with the following records:
A Record that points to 54.76.177.85
CNAME for www that points to ssl.site123.com
