It’s a good idea to add users to your Office 365 operated by 21Vianet subscription while you’re setting up your custom domain with your own email, so they’ll keep getting email sent to email addresses that use your domain name.
To start using your domain with Office 365:
This starts the wizard, and then we’ll walk you through adding your domain to your Office 365 subscription, switching your user ID (which is also your email address) to use your domain name, and setting up your users’ email addresses with your domain.
Sign in to Office 365 with your work or school account.
Choose Setup > Domains.
On the Manage domains page, choose Add domain.
Why add users now?
You can add users to Office 365 at any time. Why do it now? If you already have users getting email at your custom domain name, if you add the users and set up their addresses to use your custom domain before you finish setup, there will be no disruption in mail flow. This provides continuity for the people in your organization, for your customers, and others.
Tip: If you created users in Office 365 before you added your domain, we’ll walk you through switching those users to email addresses that use your domain name. You don’t have to add them again.
What if I don’t add users who have email addresses that use my domain?
If you haven’t added an email address that uses your domain name, and then you either change your nameserver records so that Office 365 manage your DNS records or you set up an MX record at your DNS hosting provider to point to Office 365, you’ll disrupt that user’s email. Any messages sent to that email address won’t arrive—not in the person’s current email system and not in Office 365. So be sure to add all email addresses that use your domain name to Office 365 before you flip the switch!
Until you flip the switch by either changing the name server records or the MX record to Office 365, people will continue to receive email sent to the email addresses wherever they currently get email. Once you flip the switch, email that’s sent to your domain will begin arriving in Office 365.