# smtp-blackhole
#
# waits for TCP Connections and simulates a SMTP-Server
#
# pending MultThreading

param (
    $listenport = 25
)

Set-PSDebug -Strict

Start-Transcript ".\smtp-plackhole.$(get-date -Format yyyMMdd-HHMMss).log"
Write-Host "SMTP Blackhole started"

Write-Host "Generate Listener for Port $($listenport)"
$endpoint = new-object System.Net.IPEndPoint([system.net.ipaddress]::any, $listenport)
$listener = new-object System.Net.Sockets.TcpListener $endpoint
try {
    $listener.start()   # warte auf eingehende Verbindungen 
}
catch {
    Write-Host "Error during warting listener -Quit"
    Exit
}

Write-Host "Wait for connection on Port $($listenport)"
$conn = $listener.AcceptTcpClient() # Blockiert das Skript bis eine Verbindung ankommt
$sourceip = $conn.Client.RemoteEndPoint.Address.IPAddressToString
Write-Host "Neue Verbindung von: $($sourceip)" 
$stream = $conn.GetStream()        # Binde Datenstrom
[system.io.streamreader]$streamreader = New-Object System.IO.StreamReader($stream,[system.text.encoding]::ASCII)
[system.io.streamwriter]$streamwriter = New-Object System.IO.StreamWriter($stream,[system.text.encoding]::ASCII)
$streamwriter.AutoFlush=$true

$message = "220 Welcome at SMTPBlackHole"
[string]$state = "waitforhelo"
[string]$fullmessage=""
while ($state -ne "closeconnection") {
    if ($null -ne $message){
        Write-Host "S:$($message)" -ForegroundColor Yellow
        $streamwriter.WriteLine($message)
    }
    Write-Host "Wait for Data from remote host  State:$($state)"
    try {
        $line = $streamreader.readline()
    }
    catch {
        Write-Host "Error during waiting for connection. Close"
        $line = $null
        $state = "closeconnection"
    }
    if ($null -eq $line) {
        Write-Host " Skip empty Line"
    }
    else {
        Write-Host "R:$($line)" -ForegroundColor Green
        $line = $line.ToLower()
        if ($state -eq "receivingmail"){
            Write-Host "Data:$($line)" -ForegroundColor Magenta
            if ($line -eq ".") {
                $state = "waitformailfrom"
                $message = "250 Mail accepted"
                $fullmessage
            }
            else {
                $message = $null
                $fullmessage= $fullmessage + "`r`n" +$line
                # wait for more lines and final .
            }
        }
        elseif ($line.StartsWith("quit")) {
            $message = "221 Service closing transmission channel"
            $state = "closeconnection"
        }
        else {
            switch ($state) {
                "waitforhelo" {
                    if ($line.StartsWith("helo ")) {
                        $state = "waitformailfrom"
                        $message = "250 2.0.0 Welcome $($line.substring(5)) [$($sourceip)]"
                    }
                    elseif ($line.StartsWith("ehlo ")) {
                        $state = "waitformailfrom"
                        $message = "250-Welcome $($line.substring(5)) [$($sourceip)]"
                        $message += "`r`n250-DSN"
                        $message += "`r`n250-ENHANCEDSTATUSCODES"
                        $message += "`r`n250-8BITMIME"
                        $message += "`r`n250-SIZE"
                        $message += "`r`n250 XOORG"
                    }
                    elseif ($line.StartsWith("rset")) {
                        $state = "waitformailfrom"  
                        $message = "250 2.0.0  Reset accepted"
                    }
                    else {
                        $message = "502 5.0.0 Command not implemented. Start with HELO or EHLO first"
                    }
                }
                "waitformailfrom" {
                    if ($line.StartsWith("mail from:")) {
                        $state = "waitforrcptto"
                        $message = "250 2.0.0 Hello Sender $($line.substring(10)). continue with RCPT TO"
                    }
                    elseif ($line.StartsWith("rset")) {
                        $state = "waitformailfrom"  
                        $message = "250 2.0.0  Reset accepted"
                    }                    
                    else {
                        $message = "500 5.0.0 start with MAIL FROM first"
                    }
                }
                "waitforrcptto" {
                    if ($line.StartsWith("rcpt to:")) {
                        $state = "waitfordata"
                        $message = "250 2.0.0 Message for $($line.substring(10)) OK. continue with RCPT TO or DATA"
                    }
                    elseif ($line.StartsWith("rset")) {
                        $state = "waitformailfrom"  
                        $message = "250 2.0.0  Reset accepted"
                    }                    
                    else {
                        $message = "500 5.0.0 start with RCPT TO first"
                    }
                }                
                "waitfordata" {
                    if ($line.StartsWith("data")) {
                        $state = "receivingmail"
                        #$state="closeconnection"
                        $message = "354 Start mail input; end transmission with <CRLF>.<CRLF>"
                        $fullmessage=""
                    }
                    else {
                        $message = "200 continue with RCPT TO or DATA"
                    }   
                }
                default {
                    $message = "550 State $($state) not handled. Check code"
                }
            }
        }
    }
} 

Write-Host "->$($message)"
try {
    Write-Host "Close StreamReader, Writer, Connection and Listener"
    $streamwriter.WriteLine($message)
    $streamwriter.Close()
    $streamreader.Close()
    $conn.Close()
}
catch {
    Write-Host "Connection was already closed by the remote host"
}

Write-Host "Close Listener Listener"
$listener.stop()
Stop-Transcript
Write-Host "SMTPBlackhole: End"