Add your organization's domain to Office 365 so that users can sign in with their email addresses.
1. Sign in to Office 365 portal with an admin account and open the Admin app.
2. Click Add a domain.
3. Enter a domain you own and click Next .
4. Verify by TXT record or MX Record option.
Note: It can take a day or two for your domain's DNS changes to propagate so that Office 365 can verify them.
5. Click Next.
6. Set up your online services and click Next.
7. Choose your online services and click Next.