Yes. To add subdomains, you must manage your own DNS settings at your registrar's website. If you are letting Microsoft manage your DNS settings with NS records, or if you bought the domain from Microsoft, you can't add subdomains.

Yes! To add subdomains, you must manage your own DNS settings at your registrar's website. If you are letting 21Vianet manage your DNS settings with NS records, you cannot add subdomains.

Typically, you could add up to 5,000 domains to your Microsoft 365 subscription.

For example, you could add the domains contoso.com and contosomarketing.com, and then add the subdomains www.contoso.com, www.partners.contoso.com, www.marketing.partners.contoso.com, and so on.

When you add a subdomain, it is automatically verified based on the parent domain that is being verified.

When you add multiple domains to Microsoft 365, you can host any of the services (like email) on any of the domains you add. *When you change your email to Microsoft 365, by updating a domain's MX record, ALL email sent to that domain will start coming to Microsoft 365. *

Note

If you added a contoso.com domain to a Microsoft 365 subscription, you can also add the subdomain xyz.contoso.com to another Microsoft 365 organization. When adding the subdomain, you are prompted to add a TXT record in the DNS hosting provider.

For the procedure to transfer a domain, see Transfer a domain from Microsoft to another host.

For the procedure to pilot Microsoft 365 email functionality from a custom domain to a Microsoft 365 mailbox, see Pilot Microsoft 365 from my custom domain.