I am setting up office 365 for some organizations I am working with. I have few questions regarding licensing. If a member (fully licensed with Business Premium) of organisation A needs to collaborate closely with organisation B. Does member need another license for organisation B's ? Or can he be added another way?
Other question, if one needs one license per organisation he's part of, how could we facilitate the synchronization within windows 10?
No, no license needed in this case! You can share resources to the user, and the user can exist as a guest in their AAD without a license!
There are some licensing stuff about b2b to be aware of, but the summary is, 5 external users per 1 license in your tenant Except if the guest user is already having a 365 license in that users own tenant! Read more here: