Office365 Guest Access to Shared Mailbox
Is it possible for a guest account that exists on 365 to have access to a shared mailbox? Can this be done using B2B collaboration?
I have am unable to find an exact answer from the Microsoft docs on this.
It's not possible.
The permissions can be set up only within the current organization tenant. It is not possible to set up mailbox permissions with out of tenant users
Source: Microsoft Docs