Ensure the role includes Export and Compliance Search permissions.

Before you can download mailbox data, you must ensure the administrative account has specific permissions that even a Global Administrator might not have by default.

You must assign the eDiscovery Manager or eDiscovery Administrator role to your account.

Downloading a mailbox from the typically refers to exporting its contents into a portable .pst file. This process is primarily handled through the eDiscovery tools within the Microsoft Purview compliance portal . Prerequisites for Mailbox Export

The first step is to locate and aggregate the specific mailbox data you wish to download.