It is now possible to add users from multiple domains using the User Management module.
Individual users can be added or they can be added in bulk using a csv file. This feature is only available to private cloud and on premise users.
There is configuration required on the SharePoint people picker to enable this feature. The SharePoint administrator will need to run PowerShell scripts which are provided in the upgrade documentation.
Adding Individual Users
To add an individual user, navigate to the User Management module and click on Add New.
Type in the search criteria and click on Resolve.
The dropdown will list users returned based on search criteria. Select the user, assign required permissions and then click Save.
Adding Bulk Users
To add bulk users, navigate to the User Management module and click on Bulk Add.
Select the csv containing the details of the user which need to be added. The first column in the csv which contains the username should be prepended with the domain name e.g. domainA\User1. Once the csv is selected, the adding of the users will start.