we are testing the sharing configuration in OdFB and SPO.
We configured "Users can invite new an existing guests".
In ODfB i first share a file with user firstname.lastname@example.org. He gets the invitation and then the access code.No Guest account is created.
Then i share another document with user email@example.com which is an external O365 User. This user also gets the invitation, and then the access code.
Now a Guest account is created for this user.
What is the exact algorithm behind this. are Guest users only created for O365 (School and Work Accounts)? Can I prevent that Guest Users are created at all for users invited by standard users?
It's explained in this article: https://docs.microsoft.com/en-us/sharepoint/what-s-new-in-sharing-in-targeted-release
If you have additional questions, look at this recent thread and ask them directly to Stephen.