Shared mailboxes within an Exchange/Office 365 hybrid environment are now fully functional using Full Access permissions. This has been a limitation for some customers migrating to Office 365 up until now. With this restriction removed, customers can now fully support a long term migration process or even a permanent hybrid choice for their company.
In on-premises Exchange deployments, users can be granted a variety of permissions to other user’s mailboxes. This is called delegated mailbox permissions and it is useful when someone needs to manage some part of another user’s mailbox; for example, managing an executive's calendar, or if multiple users have access to a shared repository mailbox. Some of these permissions can be used in Exchange hybrid deployments.
Exchange hybrid deployments support the use of the Full Access mailbox permission between mailboxes located in an on-premises Exchange organization and mailboxes located in Office 365. A mailbox on an on-premises Exchange server can be granted the Full Access permission to an Office 365 mailbox, and vice versa.
Note: Users might receive additional credential prompts when they first access a mailbox that is in the other realm and add it to their own Outlook profile.
While Exchange hybrid configurations do support the use of the Send-As, Receive-As, or Send on behalf of mailbox permissions, these permissions are only available when both the mailbox granting the permissions, and the mailbox receiving the permissions, are in the same realm. Any mailboxes that receive these permissions from another mailbox need to be moved at the same time as that mailbox. If a mailbox receives permissions from multiple mailboxes, that mailbox, and all of the mailboxes granting permissions to it, need to be moved at the same time and exist in the same realm of either on premises or Office 365 Exchange organizations. In addition to these permissions, the Auto Mapping feature is unsupported when used between mailboxes in the on-premises Exchange and Office 365 organizations.
Over the last few months of helping customers, I have seen where this shared mailbox access topic has been a limitation. I am happy to be able to post this material and be able to update customers that this issue has a resolution. For further reading, visit the TechNet page for additional knowledge. Thank you.