Step 1: Mange Your Own Domains

Yes you can but if and only if you mange your own domains settings at your registrar website.

    • If you letting Microsoft handle your DNS settings with Nameservers records, or you bought the domain from Microsoft, then you cannot add subdomains

Typically you can add up to 900 domain to your Office 365 subscription

Step 2: Include A Subdomain

At the point when you include a subdomain, it is naturally confirmed based on the parent domain that is being checked.

Step 3: Add Multiple Domains

At the point when you add multiple domains to Office 365, you can host any of the services such as email, on any of the domains you have included. At the point that you change your email to Office 365, by refreshing a domain MX record. All email will sent to that domain will begin coming to Office 365.