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For more information, please also see the article Working with Generic and Shared Mailboxes.
Adding a shared mailbox to new Outlook
Open Outlook.
Right-click on the account name or shared with me folder in the left navigation pane, and then choose Add shared folder or mailbox.
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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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