You can add multiple domains to Office 365, but each domain should have valid Internet domain suffix such as .com, .net, and .org.
Following are some examples of valid domains:
- contoso.com
- contos.co
- contoso.net
- contoso.us
Following are some examples of invalid domains and they cannot be added in Office 365:
- contoso (Single labeled domain is not allowed)
- contoso.local (Local domain is not allowed)
