Imagine that you’re in a project where external collaboration is needed, but first, you want to know what exactly happens when a document, site or whatever is shared with external users (users from other company, let’s say).
Firstly, someone has to send an invitation to this external user to collaborate. You have many options to select, to requiere wether user sign in or not
Secondly, the invitation arrives to the user, and he has to accept it.
Take into account that these kind of invitations remains in the request list in the site, so any admin could reject the invitation in the meantime.
Once the user, has accepted the invitationhe could access to the site with the permissions given (full control, contribute, etc…). For example, if you share a document with an external user with the permission “Full Control”, an entry is created in the “Team Site Owners” inside the site. So, you can revoke the acess by removing the user from the Owners group.
that’s all! Next day I will cover what happens with other things!
Cheers!
Albandrod's Memory 