When you try to access a SharePoint Online site by using a domain that's configured for full redelegation, the SharePoint Online site can't be accessed.
Full domain redelegation involves a domain where the name server (NS) resource records point to Office 365. To resolve this issue, follow these steps:
Verify that the NS resource records point to Office 365. To do this, use the NSlookup tool. For more information about NSlookup, click the following article number to view the article in the Microsoft Knowledge Base:
The NS resource records should point to two of the following:
If the domain was recently configured for full domain redelegation, wait 72 hours. Make sure that the SharePoint Online domain is configured from the Office 365 portal Domain management page. The SharePoint Online site should be accessed by using the address that is specified in Your SharePoint website address is. Click Change Address if the SharePoint website address is not set to your domain. If you do change this value, wait 24 hours. Then, you can access by using "www" preappended to the address. For example, if your domain is contoso.com, then you can access your SharePoint Online site as http://www.contoso.com.
Perform DNS lookup on the www CNAME record for your domain. The record should resemble the following: