<#
=============================================================================================
Name:           Find inbox rules with external email forwarding
Description:    This script Finds all inbox rules that forwards emails externally in Office 365 using PowerShell 
Website:        o365reports.com
For detailed script execution: https://o365reports.com/2022/06/09/find-office365-inbox-rules-with-external-forwarding-powershell
============================================================================================
#>

#PARAMETERS
param ( 
[string] $UserName = $null, 
[String] $Password = $null,
[Switch] $ExcludeGuestUsers
) 

#Check for ExchangeOnline module availability
$Exchange = (Get-Module ExchangeOnlineManagement -ListAvailable).Name
if ($Exchange -eq $null)
{
 Write-Host "Important: ExchangeOnline PowerShell module is unavailable. It is mandatory to have this module installed in the system to run the script successfully."  
 $Confirm = Read-Host Are you sure you want to install module? [Y] Yes [N] No  
 if ($Confirm -match "[yY]") 
 { 
  Write-Host "Installing ExchangeOnlineManagement..." -ForegroundColor Magenta
  Install-Module ExchangeOnlineManagement -Repository PSGallery -AllowClobber -Force
  Import-Module ExchangeOnlineManagement -Force
  Write-Host "ExchangeOnline PowerShell module is installed in the machine successfully." -ForegroundColor Green
 }
 else
 { 
  Write-Host "Exiting. `nNote: ExchangeOnline PowerShell module must be available in your system to run the script." 
  Exit 
 }
}

#Connecting to ExchangeOnline .......
Write-Host "Connecting to ExchangeOnline..." -ForegroundColor Cyan
if(($UserName -ne "") -and ($Password -ne ""))
{
 $SecuredPassword = ConvertTo-SecureString -AsPlainText $Password -Force
 $Credential  = New-Object System.Management.Automation.PSCredential $UserName,$SecuredPassword
 Connect-ExchangeOnline -Credential $Credential
}
else
{
 Connect-ExchangeOnline
}
Write-Host "ExchangeOnline module successfully connected..." -ForegroundColor Green

#Function for export output to CSV file
Function ExportCSV
{
 $ForwardTo = if($ForwardTo.External.count -eq 0 -and $ForwardTo.Guest.count -eq 0){"-"}else{($ForwardTo.External + $ForwardTo.Guest)-join ', '}
 $ForwardAsAttachmentTo = if($ForwardAsAttachmentTo.External.count -eq 0 -and $ForwardAsAttachmentTo.Guest.count -eq 0){"-"}else{($ForwardAsAttachmentTo.External + $ForwardAsAttachmentTo.Guest) -join ', '}
 $RedirectTo = if($RedirectTo.External.count -eq 0 -and $RedirectTo.Guest.count -eq 0){"-"}else{($RedirectTo.External + $RedirectTo.Guest) -join ', '}
 if($ForwardTo -ne "-" -or $ForwardAsAttachmentTo -ne "-" -or $RedirectTo -ne "-")
 {
  $Global:InboxRuleWithExternalEmailCount++
  $Result = @{'Mailbox Name'= $MailBoxName;'UPN'= $UPN;'Inbox Rule Name'= $_.Name;'Forward To'= $ForwardTo; 'Forward As Attachment To'= $ForwardAsAttachmentTo; 'Redirect To'= $RedirectTo}  
  $ExportResult = New-Object PSObject -Property $Result
  $ExportResult | Select-Object 'Mailbox Name','UPN','Inbox Rule Name','Forward To','Forward As Attachment To','Redirect To' | Export-CSV $OutputCsv  -NoTypeInformation -Append 
 }
}

#Getting InboxRules with external email configuration......
Write-Host "Getting InboxRules with external email configuration..."
$OutputCsv=".\InboxRuleWithExternalEmails_$((Get-Date -format MMM-dd` hh-mm` tt).ToString()).csv"
$InboxRuleCount = 0
$Global:InboxRuleWithExternalEmailCount = 0
$GuestUser = Get-MailUser -ResultSize unlimited

Get-Mailbox -ResultSize unlimited | foreach {
 
 $MailBoxName = $_.DisplayName
 $UPN = $_.UserPrincipalName
 Write-Progress -Activity "Updating...    $Global:InboxRuleWithExternalEmailCount InboxRule found with external email " -Status "Getting InboxRule from '' $MailBoxName'' mailbox"
 Get-InboxRule -MailBox $_.PrimarySmtpAddress | foreach {
  
  $InboxRuleCount++
  $ForwardTo = @{External=@();Guest=@()}
  $ForwardAsAttachmentTo = @{External=@();Guest=@()}
  $RedirectTo = @{External=@();Guest=@()}

  #ForwardTo
  if ($_.ForwardTo -ne $null )
  {
   $UserinForwardTo = ( $_.ForwardTo -split ',' )
   $ExternalUser= $UserinForwardTo | Where-Object {$_ -match "SMTP:"}
   $InternalAndGuestUser = $UserinForwardTo | Where-Object {$_ -notmatch "SMTP:"}

   #Get external users email in ForwardTo
   foreach($ExternalUsers in $ExternalUser)
   {
    $ForwardTo.External += (($ExternalUsers -split " ")[0].TrimStart('"')).TrimEnd('"') 
   }

   #Get guest users email in ForwardTo
   if(!$ExcludeGuestUsers.IsPresent)
   {
    foreach($InternalAndGuestUsers in $InternalAndGuestUser)
    {
     $InternalAndGuestUsers= (($InternalAndGuestUsers -split ":")[1])
     $GuestUser | foreach {
     
      if($InternalAndGuestUsers -eq $_.LegacyExchangeDN+"]")
      {
       $ForwardTo.Guest += $_.OtherMail
      }
     }
    }
   }
  }

  #ForwardAsAttachmentTo
  if ($_.ForwardAsAttachmentTo -ne $null )
  {
   $UserinForwardAsAttachmentTo = ( $_.ForwardAsAttachmentTo -split ',' )
   $ExternalUser = $UserinForwardAsAttachmentTo | Where-Object {$_ -match "SMTP:"}
   $InternalAndGuestUser = $UserinForwardAsAttachmentTo | Where-Object {$_ -notmatch "SMTP:"}

   #Get external users email in ForwardAsAttachmentTo
   foreach($ExternalUsers in $ExternalUser)
   {
    $ForwardAsAttachmentTo.External += (($ExternalUsers -split " ")[0].TrimStart('"')).TrimEnd('"') 
   }

   #Get guest users email in ForwardAsAttachmentTo
   if(!$ExcludeGuestUsers.IsPresent)
   {
    foreach($InternalAndGuestUsers in $InternalAndGuestUser)
    {
     $InternalAndGuestUsers= (($InternalAndGuestUsers -split ":")[1])
     $GuestUser | foreach {
     
      if($InternalAndGuestUsers -eq $_.LegacyExchangeDN+"]")
      {
       $ForwardAsAttachmentTo.Guest += $_.OtherMail
      }
     }
    }
   }
  }

  #RedirectTo
  if ($_.RedirectTo -ne $null )
  {
   $UserinRedirectTo = ( $_.RedirectTo -split ',' )
   $ExternalUser = $UserinRedirectTo | Where-Object {$_ -match "SMTP:"}
   $InternalAndGuestUser = $UserinRedirectTo | Where-Object {$_ -notmatch "SMTP:"}

   #Get external users email in RedirectTo
   foreach($ExternalUsers in $ExternalUser)
   {
    $RedirectTo.External += (($ExternalUsers -split " ")[0].TrimStart('"')).TrimEnd('"') 
   }

   #Get guest users email in RedirectTo
   if(!$ExcludeGuestUsers.IsPresent)
   {
    foreach($InternalAndGuestUsers in $InternalAndGuestUser)
    {
     $InternalAndGuestUsers= (($InternalAndGuestUsers -split ":")[1])
     $GuestUser | foreach {
     
      if($InternalAndGuestUsers -eq $_.LegacyExchangeDN+"]")
      {
       $RedirectTo.Guest += $_.OtherMail
      }
     }
    }
   }
  }

  #Export output to CSV file
  ExportCSV
 }
}
Write-Host "Script executed successfully."

#Open output file after execution
if($InboxRuleCount -eq 0)
{
 Write-Host "No InboxRule found in this organization."
}
else
{
 Write-Host "$InboxRuleCount InboxRule found in this organization." 
 if($Global:InboxRuleWithExternalEmailCount -eq 0)
 {
  Write-Host "But no InboxRule found with external email."
 }
 else
 {
  Write-Host "$Global:InboxRuleWithExternalEmailCount InboxRule found with external email."
  if((Test-Path -Path $OutputCsv) -eq "True") 
  { 
   Write-Host "The InboxRule with external email configuration report available in : $OutputCsv " -ForegroundColor Green 
   $Prompt = New-Object -ComObject wscript.shell    
   $UserInput = $Prompt.popup("Do you want to open output file?",` 0,"Open Output File",4)    
   If ($UserInput -eq 6)    
   {    
    Invoke-Item "$OutputCSV"    
   }  
  }
 }
}
  

#Clean up session
Get-PSSession | Remove-PSSession