If you want to export an Exchange mailbox database list to Excel so that you can see how large users mailboxes are, you can do this using the Exchange Management Shell (EMS).
All you need to do is to logon to your Exchange server with your mailbox database on, open up the Exchange Management Shell (EMS) and then run the following command:
Get-MailboxStatistics -Database "First Storage GroupMailbox Database" | Select DisplayName, ItemCount, TotalItemSize | Sort-Object TotalItemSize -Descending | Export-CSV C:MBSizes.csv
Press enter and this will export the data into a CSV file on the root of your Exchange Server.
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