Hi!
If you want Skype for Business Server support external users, you need to notice these tips:
*Deploying an Edge Server or Edge Pool.
*Enable the types of external user access and policies that you want to provide.
*Add the partner organization domain as a trusted domain to your Skype for Business Server and partner also need to add your domain to their Skype for Business Server as a trusted domain.
For more details about how to deploy Edge Server in Skype for Business Server, you can learn from:
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