Get-Mailbox | ForEach-Object {   $mailbox = $_.PrimarySmtpAddress
Get-InboxRule -Mailbox $mailbox | Select-Object @{Name="Mailbox";Expression={$mailbox}}, Name, Description } | Export-Csv -Path "<OutputFile>" -NoTypeInformation -Append –Force 

https://admindroid.com/how-to-manage-inbox-rules-in-exchange-online