# get-dkimselectors
#
# This script retrieves the DKIM selectors used in the last 10 messages sent by the current user.

param (
   [int64]$top=100000,
   [string]$internaldomain = "msxfaq.de",
   [string]$csvfile = ".\output\dkimselectors-$(Get-Date -Format 'yyyyMMddHHmmss').csv"
)

Write-Host "Get-DKIMSelectors Start"
Write-Host "   MaxItems: $($top)"
Write-Host "  OutputCSV: $($csvfile)"

if (!(Get-Module Microsoft.Graph)) {
   Write-Host "Microsoft.Graph module not found. Installing..." -ForegroundColor Yellow
   Install-Module Microsoft.Graph -Scope CurrentUser -Force
}
else {
   Write-Host "Microsoft.Graph module found." -ForegroundColor Green
}

if ((Get-MgContext).scopes -notcontains "Mail.Read") {
   Write-Host "# Verbinden mit meinem eigenen Postfach. Consent für Graph muss ggfls. durch Admin erfolgen"
   Connect-MGGraph -Scopes Mail.Read
}
else {
   Write-Host "Already connected to Microsoft Graph"
   Write-Host "  Username: $(Get-MgContext).account)"
   Write-Host "  Scopes  : $(Get-MgContext).scopes -join ', ')" -ForegroundColor Green
}

mkdir -Force -Path ".\output"
$result = @{}

Write-Host "Start loading messages"
$totalcount = 0
$externalcount = 0
$dkimcount = 0

#-Filter "sentDateTime ge $($(Get-Date).AddDays(-30).ToString(""o""))" `
#-Filter "$($(Get-Date).AddDays(-30).ToString(""yyyy-mm-ddThh:mm:ss""))Z" `
#    -Filter "not(endswith(/emailAddress/address,'@example.com'))" `
#    -Filter "sentDateTime ge $($(Get-Date).AddDays(-30).ToString(""yyyy-MM-ddTHH:mm:ssZ"")) and endswith(from/emailAddress/address,'someuser@example.com')" `
Get-MgUserMessage `
   -UserId ((Get-MgContext).account) `
   -Property "From,Subject,InternetMessageHeaders" `
   -Filter "sentDateTime ge $($(Get-Date).AddDays(-30).ToString(""yyyy-MM-ddTHH:mm:ssZ""))" `
   -Top $top `
| foreach-object {
   $totalcount++
   Write-host "Message ($totalcount)" -nonewline
   if ($_.From.EmailAddress.Address -eq $null) {
      Write-Host "From email null. Skip" -ForegroundColor Magenta
      return
   }  
   if ($_.From.EmailAddress.Address.endswith("@$($internaldomain)")) {
      Write-Host "internal message from $($internaldomain). Skip" -ForegroundColor Magenta
      return
   }  

   $externalcount++
   $dkimHeader = $_.internetMessageHeaders | Where-Object { $_.Name -eq "DKIM-Signature" }
   if ($dkimHeader) {
      $dkimcount++
      Write-Host "DKIM" -ForegroundColor Green -NoNewline
      foreach ($entry in $dkimheader) {
         $entryvalue = $entry.value
         Write-debug "$($entryvalue)"
         # D= extrahieren, Domain of DKIM Signature
         $d=$null
         if ($entryvalue -match "d=([^;]+)") {
            Write-host "D" -ForegroundColor Magenta -NoNewline
            $d = $Matches[1]
         }
         # S= extrahieren  Selector of DKIM Signature
         $s=$null
         if ($entryvalue -match "s=([^;]+)") {
            Write-host "S" -ForegroundColor Magenta -NoNewline
            $s = $Matches[1]
         }
         # a= extrahieren, Algorithm of DKIM Signature
         $a=$null
         if ($entryvalue -match "a=([^;]+)") {
            Write-host "E" -ForegroundColor Magenta -NoNewline
            $a = $Matches[1]
         }

         if ($d -and $s) {
            Write-host "A" -ForegroundColor Magenta -NoNewline
            $resultentry= [PSCustomObject]@{
               Mailnr = $totalcount
               From = $_.from.EmailAddress.address.split("@")[-1]
               Domain = $d
               Selector = $s
               Encryption = $a
            }
            $resultentry | export-csv $csvfile -Append -NoTypeInformation
            $key = $resultentry.From + $resultentry.Domain + $resultentry.Selector
            if ($result.ContainsKey($key)) {
               Write-Host "S" -ForegroundColor Gray -NoNewline 
            } else {
               $result[$key] = @($resultentry)
               Write-Host "`n Added Domain $($resultentry.Domain) with Selector $($resultentry.Selector)" -ForegroundColor Cyan -NoNewline
            }
         }
      }
   }
   Write-Host " Done"
}
Write-Host "Done loading messages. Found $($result.Count) unique DKIM selectors." -ForegroundColor Green
Write-Host "Total messages processed     : $totalcount"
Write-Host "External messages processed  : $externalcount"
Write-Host "Messages with DKIM signatures: $dkimcount"   

$result.Values | Format-Table -AutoSize