Export the PowerShell output to a text file in tab-delimited format

Use the Export-CSV with a tab delimiter. Note, that you can’t use the output of format-table as an input to export-CSV, use select-object instead:

Get-MailboxStatistics -Database data01 |
  select displayname,databasename,itemcount,totalitemsize |
  export-csv -delimiter "`t" -path theOutFile.txt -notype