Add or edit custom DNS records in Office 365
Check the Domains FAQ if you don't find what you're looking for.
Sign in to the admin center at https://admin.microsoft.com.
Go to the Settings > Domains page.
On the Domains page, select a domain.
Under DNS settings, select Custom Records, and then select New custom record.
Select the type of DNS record you want to add, and type the information for the new record.