smtp-relay/tests/smtpclient/Program.cs

using System.Data;
using System.Net;
using System.Net.Mail;
using System.Net.Sockets;
using System.Text;

namespace SmtpClient;

internal class Program
{
    private static string? _host = null;
    private static string? _username = null;
    private static string? _password = null;
    private static string? _from = null;
    private static List<string>? _rcpts = [];
    private static List<string>? _rcptsCc = [];
    private static string? _subject = null;
    private static string? _body = null;
    private static bool _secure = false;

    static async Task Main()
    {
        Console.WriteLine("Relay Test Client");

        Console.WriteLine("\nSelect Input:");
        Console.WriteLine("\t1-Static");
        Console.WriteLine("\t2-Interactive");

        switch (Console.ReadKey().Key)
        {
            case ConsoleKey.D1:
            case ConsoleKey.NumPad1:
                StaticInput();
                break;
            case ConsoleKey.D2:
            case ConsoleKey.NumPad2:
                InteractiveInput();
                break;
            default:
                return;
        }

        Console.WriteLine("\nSelect Method:");
        Console.WriteLine("\t1-Single Mail");
        Console.WriteLine("\t2-Single Mail (Raw Pipelined)");
        Console.WriteLine("\t3-Mutli Mail");

        try
        {
            switch (Console.ReadKey(true).Key)
            {
                case ConsoleKey.D1:
                case ConsoleKey.NumPad1:
                    await SendAsync();
                    break;
                case ConsoleKey.D2:
                case ConsoleKey.NumPad2:
                    await SendPipelinedAsync();
                    break;
                case ConsoleKey.D3:
                case ConsoleKey.NumPad3:
                    await SendMultiAsync();
                    break;
                default:
                    Console.WriteLine("\nUndefined Method");
                    break;
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.ToString());
        }
    }

    static void StaticInput()
    {
        _host = "localhost:2525"?.Trim();
        _secure = false;
        _username = "relay@example.local";
        _password = "supersecret";
        _from = "me@example.local"?.Trim();
        _rcpts = "noreply@example.local"?.Trim()?.Split(';').ToList();
        _rcptsCc = [];
        _subject = "Testnachricht";
        _body = "Das ist eine Testnachricht.";
    }

    static void InteractiveInput()
    {
        Console.WriteLine("\nEnter Relay Host: ");
        _host = Console.ReadLine()?.Trim();

        Console.WriteLine("\nEnter Username (Optional): ");
        _username = Console.ReadLine()?.Trim();

        if (!string.IsNullOrWhiteSpace(_username))
        {
            Console.WriteLine("\nEnter Password: ");
            _password = Console.ReadLine()?.Trim();
        }

        Console.WriteLine("\nEnter Sender:");
        _from = Console.ReadLine()?.Trim();

        Console.WriteLine("\nEnter Receiver (delimit with ';'):");
        _rcpts = Console.ReadLine()?.Trim()?.Split(';').ToList();

        Console.WriteLine("\nEnter Cc Receiver (delimit with ';'):");
        _rcptsCc = Console.ReadLine()?.Trim()?.Split(';').ToList();

        Console.WriteLine("\nEnter Subject:");
        _subject = Console.ReadLine()?.Trim();

        Console.WriteLine("\nEnter Body:");
        _body = Console.ReadLine()?.Trim();
    }

    static async Task SendAsync()
    {
        var from = new MailAddress(_from!);
        var to = _rcpts!.Select(p => new MailAddress(p)).ToList();
        var cc = _rcptsCc!.Select(p => new MailAddress(p)).ToList();

        var firstTo = to.First();
        to.Remove(firstTo);

        using var message = new MailMessage(from, firstTo)
        {
            Priority = MailPriority.Normal,
            Subject = _subject ?? "Undefined",
            IsBodyHtml = false,
            Body = _body ?? string.Empty,
        };

        foreach (var x in to)
            message.To.Add(x);

        foreach (var x in cc)
            message.CC.Add(x);

        message.Attachments.Add(new Attachment("attachment.txt"));

        var credential = new NetworkCredential();

        if (!string.IsNullOrWhiteSpace(_username))
        {
            credential.UserName = _username;
            credential.Password = _password;
        }

        var host = _host;
        var port = 25;

        if (_host!.Contains(':'))
        {
            host = _host.Split(':')[0];
            port = int.Parse(_host.Split(":")[1]);
        }

        using var smtp = new System.Net.Mail.SmtpClient(host, port)
        {
            UseDefaultCredentials = false,
            Credentials = credential,
            EnableSsl = _secure,
            DeliveryMethod = SmtpDeliveryMethod.Network
        };

        await smtp.SendMailAsync(message);
    }

    static async Task SendMultiAsync()
    {
        var from = new MailAddress(_from!);
        var to = _rcpts!.Select(p => new MailAddress(p)).ToList();
        var cc = _rcptsCc!.Select(p => new MailAddress(p)).ToList();

        var firstTo = to.First();
        to.Remove(firstTo);

        using var message = new MailMessage(from, firstTo)
        {
            Priority = MailPriority.Normal,
            Subject = _subject ?? "Undefined",
            IsBodyHtml = false,
            Body = _body ?? string.Empty
        };

        foreach (var x in to)
            message.To.Add(x);

        foreach (var x in cc)
            message.CC.Add(x);

        message.Attachments.Add(new Attachment("attachment.txt"));

        var credential = new NetworkCredential();

        if (!string.IsNullOrWhiteSpace(_username))
        {
            credential.UserName = _username;
            credential.Password = _password;
        }

        var host = _host;
        var port = 25;

        if (_host!.Contains(':'))
        {
            host = _host.Split(':')[0];
            port = int.Parse(_host.Split(":")[1]);
        }

        using var smtp = new System.Net.Mail.SmtpClient(host, port)
        {
            UseDefaultCredentials = false,
            Credentials = credential,
            EnableSsl = _secure,
            DeliveryMethod = SmtpDeliveryMethod.Network
        };

        await smtp.SendMailAsync(message);
        await smtp.SendMailAsync(message);
    }

    static async Task SendPipelinedAsync()
    {
        var raw = "EHLO SmtpClient\r\n";

        if (!string.IsNullOrWhiteSpace(_username))
        {
            raw += $"AUTH PLAIN {Convert.ToBase64String(Encoding.UTF8.GetBytes($"\0{_username}\0{_password}"))}\r\n";
        }

        raw += $"MAIL FROM:<{_from}> SIZE=512\r\n";

        foreach (var rcpt in _rcpts!)
        {
            raw += $"RCPT TO:<{rcpt}>\r\n";
        }

        raw += "DATA\r\n";
        raw += "MIME-Version: 1.0\r\n";
        raw += $"From: {_from}\r\n";
        raw += $"To: {string.Join(", ", _rcpts!)}\r\n";

        if (_rcptsCc != null && _rcptsCc.Count > 0)
        {
            raw += $"Cc: {string.Join(", ", _rcptsCc!)}\r\n";
        }

        raw += "Date: 29 Oct 2025 21:10:56 +0100\r\n";
        raw += $"Subject:{_subject}\r\n";
        raw += "\r\n" ;
        raw += $"{_body}";
        raw += "\r\n.\r\n";
        raw += "QUIT\r\n";

        var bytes = Encoding.ASCII.GetBytes(raw);
        var sock = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);

        var host = _host;
        var port = 25;

        if (_host!.Contains(':'))
        {
            host = _host.Split(':')[0];
            port = int.Parse(_host.Split(":")[1]);
        }

        await sock.ConnectAsync(host!, port);
        await sock.SendAsync(bytes);

        Console.WriteLine("wait 3 seconds...");
        await Task.Delay(3000);
    }
}