Exchange share a folder with a blocked suser
It's not possible to access a Mailbox of a disabled user. In order to do so, you have to convert the users mailbox into a shared ressource. You can use Set-Mailbox to do that:
Set-Mailbox -Identity <MailboxIdentity> -Type Shared
The user account for this Mailbox will stay disabled. Bonus: This will convert the Mailbox into a license free ressource.