Hello,
Thank you for your question. InMotion Hosting does not support domain masking. The closest you will have is to set the domain as either a parked domain or a redirect. Redirects and Parked domains will work exactly the same in that the visitor can use the alias domain name but as soon as they arrive on the site, the true domain name will be revealed.
The only difference in the two is whenParked domains are used on the primary domain name for the account, the domain name in the URL bar will not change from the alias. This is the closest to domain masking our systems get.
Kindest Regards,
Scott M