Hi @Cranbin
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For shared mailboxes, shared mailboxes are used when multiple people need to access the same mailbox, such as company information or support email addresses, reception desks, or other features that may be shared by multiple people.
For details about how to create one, see this topic: https://learn.microsoft.com/en-us/microsoft-365/admin/email/create-a-shared-mailbox?view=o365-worldwide.
A shared folder is when you have been granted the appropriate permissions to someone else's mailbox, you can access that person's mailbox. More information, see: Share and access another person's mailbox or folder in Outlook.
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