Run the Get-MailboxStatistics Exchange Management Shell in Exchange server as below to get the output;

Get-MailboxStatistics -server srv-exch | Sort-Object TotalItemSize –Descending | ft DisplayName,@{ expression={$_.TotalItemSize.Value.ToKB()}},ItemCount

  • Value.To.MB – Generate in MegaBytes
  • My server name – srv-exch (put your server name)
  • Ascending or Descending – Do your choice

Get-MailboxStatistics -server srv-exch | Sort-Object TotalItemSize –Descending | ft DisplayName,@{ expression={$_.TotalItemSize.Value.ToKB()}},ItemCount > c:\temp\mailboxstats.txt

Where you can get text file in the path c:\temp\mailboxstats.txt