If you want to search Exchange log for a particular subject, or just a bite of it, you can search witch this commands.
This will also export it to a nice CSV files.
Get-MessageTrackingLog -resultsize unlimited | Where-object {$_.MessageSubject -like "*Kenneth Dalbjerg"} | select-object timestamp,Sender,@{l="Recipients";e={$_.Recipients -join " "}},messageSubject | export-csv c:\KennethDalbjerg.csv
if you want to export all you mailboxes sizes to CSV/Excel, you can run this command in you powershell:
get-mailbox | get-mailboxstatistics | select-object displayname, itemcount, totalitemsize | export-csv c:\mailbox-size.txt
Howto Export all mailbox’es and there size to a CSV file
get–mailbox | get-mailboxstatistics | select-object DisplayName,TotalItemSize,StorageLimitStatus,LastLogonTime | Export-Csv c:\exchange.csv