External Sharing

Thanks,

But MS support articles say explicitly "An external user invitation doesn't require that it be accepted by the email address to which it was first sent. It is a one-time invite"

In this article it pretty clearly says that invitations can be forwarded and someone else can use other account:

"Only one person may log in to access your site or document using an invitation you send. However, the person who gets your invitation may decide to not use it, and instead forward the invitation to someone else who can then log in using their Microsoft account or work account to access the site or document."

https://support.office.com/en-us/article/Share-sites-or-documents-with-people-outside-your-organization-80e49744-e30f-44db-8d51-16661b1d4232

This is what bothers me now, because if I recall correctly, previously it worked in a way that you could send the invitation to any email address, and then the receiver could use one of his/hers Microsoft Accounts (Office 365 from work, private outlook.com or private Office 365 account).

I might only know external user's work email address and share the site using that email. I cannot know if that email address is tied or not to any MS accounts.