Windows Azure Active Directory (WAAD) is a multi-tenant cloud-based identity management service offered by Microsoft. WAAD is used by many services of Microsoft like Office 365, Exchange Online and Windows Azure.
WAAD is used for authentication to Office 365, to Microsoft Azure and SaaS applications.
It allows for synchronization of local / on-premise Microsoft Active Directory accounts and security groups to WAAD. At creation a Azure Active Directory has a default domain name like contoso.onmicrosoft.com
To be able to authenticate using a customer owned domain account like email@example.com , so called custom domains can be added by customers to a Azure AD.
Customers adding their domain must prove they own the domain. This is proved by adding a record to the DNS server which is master for their domain.
During verification of this domain an error is shown ‘could not verify the domain’
To check the records of your domain services like http://dnsquery.org/ can be used. This made clear the MX and TXT records were not actually added to the DNS server.
It was solved in my situation by not typing in the @ sign in the host/name field of the DNS register form of my domain registar. For some reason any record I added which had a @ in the name field was not added. The webinterface however did not shown an error indicating an invalid input.
When I used the name of the domain instead of @ , the domain verify was succesfull within minutes.