After few months in preview, the Azure AD External Collaboration policy is now available in GA with easier way to manage.
In preview mode you had to use PowerShell to setup and manage the external collaboration policy, with the GA you can now use the Azure Administration portal, making things a little bit easier.
To enable and manage Azure AD External Collaboration policy go to Azure AD management portal (https://aad.portal.azure.com) or Azure management portal (https://portal.azure.com) and reach out your Azure Active Directory configuration blade
From there access the User Setting blade and reach out the External Users management link
From this configuration blade you will find the already well known guest management options (permissions, who can invite…) but also the new External Collaboration Policy under the Collaboration Restrictions
By default, there is no restriction
Then if you enabled one of the restriction options you will be able to define the domain you want to authorize/block the external sharing with.
You can add up to 60 domains and once configured the restriction will also apply to Office 365 Teams and Groups.
You add one domain per line (being automatically displayed)