Using an Inbound shared mailbox
Creating an inbound shared mailbox
See https://learn.microsoft.com/en-us/microsoft-365/admin/email/create-a-shared-mailbox?view=o365-worldwide for more information on how to create a shared mailbox in Microsoft 365.
Using an inbound shared mailbox for email processing
To set this up go to Messaging > Message Sources and press 'create'
Select 'Sign in with Microsoft'