In the left menu, click Show More if it's not already expanded.
Click Setup > Domains.
Click Add domain.
Enter the domain name and then click Next.
On the Verify domain page a TXT record is displayed to verify ownership of the domain. The TXT record is added through your DNS host.
If hosting DNS through Winhost, log into the Winhost Control Panel, click Domains, then the Manage link for the applicable domain. Then Add the TXT Record. If you require assistance with the TXT record update, please feel free to contact Support.
When the record is added, you may need to wait an hour or two for it to propagate. After propagation has completed, click the Verify button in the Office 365 Admin center.
After verifying the domain, select I'll manage my own DNS records and click Next.
Select the applicable services and click Next for the DNS records necessary for Office 365.
Like the domain verification, once the provided DNS records have been added and propagated, click Verify. Or if you have existing records and want to make the DNS record updates at a later time, check Skip this step and then click Skip.