You can't sign in to Skype for Business Online by using a domain that is configured for full redelegation
When you try to sign in to Skype for Business Online (formerly Lync Online) in Office 365 as an Office 365 Business customer who has a custom verified domain, you receive an error message that indicates that the server is temporarily unavailable.
Office 365 Business customers who have custom verified domains have those domains fully redelegated to Office 365. "Full domain redelegation" indicates a domain for which the name server (NS) resource records point to Office 365. Therefore, the Domain Name System (DNS) records that are required for Office 365 functionality are managed by Office 365.
To fix this problem, follow these steps:
Make sure that the NS resource records point to Office 365. To do this, use the Nslookup tool to query the name server records for your domain. The NS resource records should point to two of the following fully qualified domain names (FQDNs):
If the domain was recently configured for full domain redelegation, you should wait for 72 hours before you run a query.
If you still can’t sign in after the NS resource records have been changed, there may be a delay in publishing the Skype for Business Online DNS records. If this occurs, test the DNS records. To do this, follow these steps:
- Browse to the Microsoft Remote Connectivity Analyzer website.
- Click the Office 365 tab.
- Under Microsoft Lync Tests, click Office 365 Lync DNS Test, and then click Next.
- Enter the address that you use to try to sign in to Skype for Business Online (for example, email@example.com), and then start the test.
This test examines all four DNS records that are required by Skype for Business Online to determine whether they're correctly configured. The results of the test will resemble the following output.
If the NS records and the Lync Service (SRV) records are correct, perform standard Lync sign-in troubleshooting. For more information, go to the following Microsoft Knowledge Base article:2541980 How to troubleshoot sign-in issues in Skype for Business Online
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