Find accounts with mail forwarding

Connect-ExchangeOnline -ShowBanner:$False -ErrorAction Stop

[array]$Modules = Get-Module
If ("ExchangeOnlineManagement" -notin  $Modules.Name) {
   Connect-ExchangeOnline -ShowBanner:$False -ErrorAction Stop
}
 
Write-Host "Finding user and shared mailboxes..."
[array]$Mbx = Get-ExoMailbox -RecipientTypeDetails UserMailbox, SharedMailbox -Properties ForwardingSmtpAddress -ResultSize Unlimited
If (!$Mbx) {
   Write-Host "No user or shared mailboxes found!" -ForegroundColor Yellow
   Break
} Else {
   Write-Host ("{0} user and shared mailboxes found" -f $Mbx.Count) -ForegroundColor Green
}
 
$Report = [System.Collections.Generic.List[Object]]::new()
Clear-Host; $MbxNumber = 0
ForEach ($M in $Mbx) {
    $MbxNumber++
    $ProgressBar = "Checking mailbox " + $M.DisplayName + " (" + $MbxNumber + " of " + $Mbx.Count + ")"
    Write-Progress -Activity "Looking for forwarding settings and inbox rules" -Status $ProgressBar -PercentComplete ($MbxNumber/$Mbx.Count*100)
    $Rule = $Null
    If ($null  -ne $M.ForwardingSmtpAddress) { # Mailbox has a forwarding address
         $ReportLine = [PSCustomObject]@{
            Mailbox           = $M.DisplayName
            UPN               = $M.UserPrincipalName
            "Mailbox type"    = $M.RecipientTypeDetails
            ForwardingAddress = $M.ForwardingSmtpAddress.Split(":")[1]
            InboxRule         = "N/A"
            "Rule Removed"    = "N/A"
            Enabled           = "N/A"}
       $Report.Add($ReportLine)
    }
    [array]$InboxRules = (Get-InboxRule -Mailbox $M.ExternalDirectoryObjectId | Where-Object {$_.ForwardTo -or $_.ForwardAsAttachmentTo -or $_.RedirectTo})
    If ($null -ne $InboxRules) {
       Write-Host "Processing inbox rules"
       ForEach ($Rule in $InboxRules) {
          $Ex = $null
          $ForwardTo = @()
          $ForwardTo = ($Rule.ForwardTo | Where-Object { ($_ -Match "SMTP") -or ($_ -Match "EX:") } )
          $ForwardTo += ($Rule.ForwardAsAttachmentTo | Where-Object {($_ -Match "SMTP") -or ($_ -Match "EX:")})
          $ForwardTo += ($Rule.RedirectTo | Where-Object {($_ -Match "SMTP") -or ($_ -Match "EX:")})
          If ($ForwardTo.Count -gt 0) {
             ForEach ($Recipient in $ForwardTo) {
                If ($Recipient -Match "EX:") {
                   # Recipient known in Exchange directory
                   $Ex = (Get-Recipient -Identity ($Recipient-Split "Ex:")[1].trim("]}"))
                   $EmailAddress = $Ex.PrimarySmtpAddress }
                Else  {
                  # Simple SMTP address
                   $EmailAddress = ($Recipient -Split "SMTP:")[1].Trim("]")
                   $Ex = (Get-Recipient -Identity $EmailAddress) }
             }
 
             Write-Host $M.RecipientTypeDetails $M.DisplayName "has a rule to forward email to" $EmailAddress -ForegroundColor Red
             # Remove the rule if the address is unknown to the directory
             If ($null -eq $Ex) {
                 Remove-InboxRule -Identity $Rule.Identity -Confirm:$False; $RuleRemoved = "Yes"
                 Write-Host "Rule" $Rule.Name "removed from mailbox!" }
             Else {
                 Write-Host "Destination is known to the tenant directory. Please remove" $Rule.Name "manually if necessary"; $RuleRemoved = "No" }
 
             $ReportLine = [PSCustomObject]@{
                Mailbox           = $M.DisplayName
                UPN               = $M.UserPrincipalName
                "Mailbox type"    = $M.RecipientTypeDetails
                ForwardingAddress = $EmailAddress
                InboxRule         = $Rule.Name
                "Rule Removed"    = $RuleRemoved
                Enabled           = $Rule.Enabled}
             $Report.Add($ReportLine) }
       }
     }
}
[array]$InboxRulesFound = $Report | Where-Object {$_.InboxRule -ne "N/A"}
[array]$MailForwarding  = $Report | Where-Object {$_.InboxRule -eq "N/A"}
$MailboxesWithRules = $InboxRulesFound.Mailbox -join ", "
$MailboxesForwarding =  $Mailforwarding.Mailbox -join ", "
Write-Host ("{0} mailboxes found with forwarding addresses: {1}; {2} mailboxes found with forwarding inbox rules: {3}" -f $MailForwarding.Count, $MailboxesForwarding, $InboxRulesFound.Count, $MailboxesWithRules)