AD flag for internal and external colleges

Hey,

we use only the Azure AD for exchange, Lync and SharePoint. We do not use a on premise AD. All AD managing in the cloud. 

Now we have internal and external workers (freelancer). How I can setup a AD attribute in Azure AD to show if the college an internal or external college?

In exchange online we want set up dynamically distribution groups (on for all team members, one for all internal colleges and one for all external colleges). Is there a other way to do this then a AD flag?

Thanks for help

Stefan