Für bestimmte Aufgaben ist es notwendig einen Mail-Proxy zu konfigurieren. Dies lässt sich relativ einfach mit einem NGINX-Server und dem dazugehörigen Mail-Modul erledigen. Im Video zeige ich den ganzen Konfigurationsprozess.

Die Quellen zu den Links im Video finden Sie hier

• Netcup Server Gutscheine - http://netcup.renefuerst.eu
• NGINX Kurs und andere Kurse im Angebot - https://www.renefuerst.eu/sale/
• Proxy Example https://www.nginx.com/resources/wiki/start/topics/examples/imapproxyexample/
• IMAP Authenticate https://www.nginx.com/resources/wiki/start/topics/examples/imapauthenticatewithapachephpscript/
• https://ssl-config.mozilla.org/

NGINX-Pakete die notwendig sind

Debian / Ubuntu basierte Systeme:
apt install nginx-full nginx-common libnginx-mod-mail php-fpm certbot

Redhat / CentOS basierte Systeme:
yum install epel-release
yum install nginx nginx-mod-mail

nginx.conf

mail {
  auth_http  localhost/auth.php;
  pop3_capabilities  "TOP"  "USER";
  imap_capabilities  "IMAP4rev1"  "UIDPLUS";

  server {
    listen     110;
    protocol   pop3;
    proxy      on;
  }

  server {
    listen     25;
    protocol   smtp;
    proxy      on;
  }

  server {
    listen     143;
    protocol   imap;
    proxy      on;
  }

auth.php

<?php
/*
NGINX sends headers as
Auth-User: somuser
Auth-Pass: somepass
On my php app server these are seen as
HTTP_AUTH_USER and HTTP_AUTH_PASS
*/
if (!isset($_SERVER["HTTP_AUTH_USER"] ) || !isset($_SERVER["HTTP_AUTH_PASS"] )){
  fail();
}

$username=$_SERVER["HTTP_AUTH_USER"] ;
$userpass=$_SERVER["HTTP_AUTH_PASS"] ;
$protocol=$_SERVER["HTTP_AUTH_PROTOCOL"] ;

// default backend port
$backend_port=110;

if ($protocol=="imap") {
  $backend_port=143;
}

if ($protocol=="smtp") {
  $backend_port=25;
}

// NGINX likes ip address so if your
// application gives back hostname, convert it to ip address here
$backend_ip["mailhost01"] ="192.168.1.22";
$backend_ip["mailhost02"] ="192.168.1.33";

// Authenticate the user or fail
if (!authuser($username,$userpass)){
  fail();
  exit;
}

// Get the server for this user if we have reached so far
$userserver=getmailserver($username);

// Get the ip address of the server
// We are assuming that you backend returns hostname
// We try to get the ip else return what we got back
$server_ip=(isset($backend_ip[$userserver]))?$backend_ip[$userserver] :$userserver;

// Pass!
pass($server_ip, $backend_port);

//END

function authuser($user,$pass){
  // password characters encoded by nginx:
  // " " 0x20h (SPACE)
  // "%" 0x25h
  // see nginx source: src/core/ngx_string.c:ngx_escape_uri(...)
  $pass = str_replace('%20',' ', $pass);
  $pass = str_replace('%25','%', $pass);

  // put your logic here to authen the user to any backend
  // you want (datbase, ldap, etc)
  // for example, we will just return true;
  return true;
}

function getmailserver($user){
  // put the logic here to get the mailserver
  // backend for the user. You can get this from
  // some database or ldap etc
  // dummy logic, all users that start with a,c,f and g get mailhost01
  // the others get mailhost02
    return "mailhost01";
}

function fail(){
  header("Auth-Status: Invalid login or password");
  exit;
}

function pass($server,$port){
  header("Auth-Status: OK");
  header("Auth-Server: $server");
  header("Auth-Port: $port");
  exit;
}

SSL-Configuration in der nginx.conf

  starttls  on; ## enable STARTTLS for all mail servers
  ssl_prefer_server_ciphers  on;
  ssl_protocols              TLSv1 SSLv3;
  ssl_ciphers                HIGH:!ADH:!MD5:@STRENGTH;
  ssl_session_cache          shared:TLSSL:16m;
  ssl_session_timeout        10m;
  ssl_certificate            /folder/to/ssl/fullchain.pem;
  ssl_certificate_key        /folder/to/ssl/private/privkey.pem;
  ssl_dhparam                /etc/ssl/certs/dhparam.pem 

NGINX-Kompilierung mit Modulen für Mail

./configure --with-mail --with-mail_ssl_module