In case you are facing an "Please enter a valid email" error while signing-in (see the image below), it means that your Azure Active Directory (AAD) tenant domain has not been added to our authentication solution.
To resolve this issue, please provide the following information by Submitting a request through the Knowledgebase to our Support :
- Customer Name
- Azure AD domain (xxx.onmicrosoft.com)
- Alias Domains* (alternative domain names: xx1.onmicrosoft.com, xx2.onmicrosoft.com, etc.)
To find out which domains are the valid ones, you may as well ask your company's Global Administrator to provide a list of domains configured in the O365 Admin Center: