Over the summer, Google added a new feature to give Google Apps administrators the ability to whitelist other domains to interact with their domain on apps such as Google Drive and Classroom. This was a highly requested feature for Classroom as a number of schools have their students on a separate GAFE domain than their staff. Schools in that situation could not easily use Classroom until now. I have received numerous emails asking how to configure this, so I thought I would write a post on how it works.
1. First, you need to whitelist the domain you want to have interact with Classroom in your GAFE domain. You can do this in the Admin console by going to Domains > Whitelisted external domains. If you do not see the Domains option, it is likely under More Controls at the bottom of the Admin console homescreen.
NOTE: You can also get to this same location by going to Apps > Google Apps > Classroom > Whitelisted domains. Then click on the configure link. If a domain has already been whitelisted, it will be an edit link instead.
2. Then type in the GAFE domain you want to whitelist and click the ADD button. You can whitelist as many domains as needed. If any of these domains have subdomains or alias that also need whitelisted, you will need to add them separately.
3. After you have whitelisted the GAFE domain(s) you want to have interact with Google Classroom on your domain, you then need to set the permissions for it. You do this by going to Apps > Google Apps > Classroom > Whitelisted domains. Then check the two checkbox options as appropriate for your situation.
That is how you whitelist domains for Classroom. One last thing to remember is that the whitelisted domain will also need to do this in their Admin console for your domain. This is necessary for Classroom to work properly between the domains.