"Unable to sign in to service" error after you remove a custom domain in the Office 365 environment

Consider the following scenario. You create a custom domain in the�Office 365 environment. You also create SRV records both for Auto-Discovery and for Federation in Domain Name System (DNS) for the custom domain. You do this so that Microsoft Lync clients can locate the Microsoft Lync Online service by referencing the user-specified SIP URI. However, after you remove the custom domain from the�Office 365 environment, some Microsoft Lync clients receive the following error message:

This issue occurs when you remove the custom domain but you do not remove the corresponding AutoDiscovery SRV record from DNS. In this situation, the Microsoft Lync client uses the Auto-Discovery SRV record to discover the Microsoft Lync Online service. However, the Lync client cannot connect to the Lync Online service because the requested domain is not recognized.

To resolve this issue, remove the AutoDiscover SRV record from DNS.