Mock Mail Server & Client

MockMailServerAndClient.cs

using SmtpServer.ComponentModel;
using SmtpServer;
using MimeKit;
using MailKit.Net.Smtp;
using SmtpServer.Storage;
using System.Buffers;


// **PREREQUIRED: ADD '127.0.0.1 aaa.bbb' to HOSTS file.

var options = new SmtpServerOptionsBuilder()
    .ServerName("aaa.bbb")
    .Port(25, 587)
    .Build();

var sp = new ServiceProvider();
sp.Add(new SampleMessageStore());

var smtpServer = new SmtpServer.SmtpServer(options, sp);

_ = smtpServer.StartAsync(CancellationToken.None);


var message = new MimeMessage();
message.From.Add(new MailboxAddress("Joey Tribbiani", "joey@aaa.bbb"));
message.To.Add(new MailboxAddress("Orlys Ma", "orlys@aaa.bbb"));
message.Subject = "How you doin'?";

message.Body = new TextPart("plain")
{
    Text = 
    """

        Hey Orlys,
        
        I just wanted to let you know that Monica and I were going to go play some paintball, you in?
        
        -- Joey
    """
};

using (var client = new SmtpClient())
{
    client.Connect("aaa.bbb", 587, false);

    // Note: only needed if the SMTP server requires authentication
    //client.Authenticate("joey", "password");

    client.Send(message);
    client.Disconnect(true);
}

Console.ReadKey();



public class SampleMessageStore : MessageStore
{
    public override async Task<SmtpServer.Protocol.SmtpResponse> SaveAsync(ISessionContext context, IMessageTransaction transaction, ReadOnlySequence<byte> buffer, CancellationToken cancellationToken)
    {
        await using var stream = new MemoryStream();

        var position = buffer.GetPosition(0);
        while (buffer.TryGet(ref position, out var memory))
        {
            await stream.WriteAsync(memory, cancellationToken);
        }

        stream.Position = 0;

        var message = await MimeMessage.LoadAsync(stream, cancellationToken);
        await Console.Out.WriteLineAsync("FROM:" + string.Join(",", message.From));
        await Console.Out.WriteLineAsync("TO:" + string.Join(",", message.To));
        await Console.Out.WriteLineAsync("CONTENT:" + message.TextBody);

        return SmtpServer.Protocol.SmtpResponse.Ok;
    }
}