Exchange 2010: Create list mailbox sizes (PS)
Create list Exchange 2010 mailbox size (PowerShell)
For just 1 mailbox database:
Get-MailboxStatistics -Database "Mailbox Database Name" | Select DisplayName, ItemCount, TotalItemSize | Sort-Object TotalItemSize -Descending | Export-CSV C:\TEMP\RPT_DB_Mailbox_Size.csv
For the entire server:
Get-MailboxStatistics -Server "Server Name" | Select DisplayName, ItemCount, TotalItemSize | Sort-Object TotalItemSize -Descending | Export-CSV C:\TEMP\RPT_SVR_Mailbox_Size.csv