You select services to use with your domain when you’re adding the domain to Office 365 operated by 21Vianet. You select services to use with your domain when you’re adding the domain to Microsoft 365. Microsoft 365 uses this information to show you the list of just the DNS records (such as an MX record) that you’ll need to create or update at your DNS host website, so that Microsoft 365 services will work.
Knowing which services you’re using, Microsoft 365 shows you only the DNS records that apply to you, keeping the list shorter and less confusing.
I don’t see DNS records for some services on the DNS management page
You might see DNS records for only some services on the DNS management page. That’s expected if you selected only some Microsoft 365 services.
Tips: To see the DNS management page for one of your domains:
Sign in to Microsoft 365 with your work or school account.
Choose Setup > Domains.
On the Manage domains page, choose a domain in the list, and then choose Manage DNS.
For example, if you selected Exchange Online, you’ll see, in the domains setup wizard wizard and on the DNS management page, only the DNS records you have to update for Exchange Online. These include the records to send email to Microsoft 365, set up Autodiscover, and so on. Based on your selection, Microsoft 365 (in this scenario) shows only the records for Exchange Online, not for the other services, such Skype for Business Online.