Your initial email address in Office 365 operated by 21Vianet includes .partner.onmschina.cn, like email@example.com. You can change it to a friendlier address like firstname.lastname@example.org. You'll need your own domain name, like fourthcoffee.com first. If you already have one, great! If not, you can learn how to buy one from a domain registrar.
Then set it up by doing the following.
Sign in to Office 365 with your work or school account.
Choose Setup > Domains.
On the Manage domains page, choose Add domain.
Follow the steps to confirm that you own your domain and to change your email address.
You’ll be guided to get everything set up correctly with your domain in Office 365.
Want to see the steps first? Check out the video: