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Notes:
The mailbox folders and contents can take an hour or two to appear if your permission to access the shared mailbox was added on the same day when you add the shared mailbox to Outlook.
Sent messages from this shared mailbox will be saved in the Shared Mailboxes' users Sent folder
To learn more, please refer to the article https://support.microsoft.com/en-us/office/open-and-use-a-shared-mailbox-in-outlook-d94a8e9e-21f1-4240-808b-de9c9c088afd
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