To use your domain with Office 365, you don’t transfer it to Office 365 operated by 21Vianet,. Instead, to use your domain name in Office 365, you go through a process where you add your domain to Office 365, prove that you own it, and then update your domain’s DNS records to associate it with your Office 365 services, such as Exchange Online for your email. Learn about how to add your custom domain to Office 365.
Your relationship with your current domain registrar doesn’t change. You continue to send your payments to them for domain renewals. That's because domain transfer refers to the process of changing the registrar for a domain. When you transfer a domain, you change who you send payments to in order to renew and keep your domain name.
For example, if your domain is registered at a registrar that doesn't support all the DNS record types that are required in Office 365, you could transfer your domain to a different registrar. To transfer a domain, go to the registrar where you want your site, search their website for "transfer," and follow the directions.
If you would like to use a different Office 365 plan, see Switch to a different Office 365 for business plan.