SmtpServer is a lightweight yet powerful SMTP server implementation in C#.
Built entirely in .NET, it leverages the Task Parallel Library (TPL) for maximum performance.
Check the Changelog
SmtpServer currently supports the following extensions:
- STARTTLS
- SIZE
- PIPELINING
- 8BITMIME
- SMTPUTF8
- AUTH PLAIN LOGIN
The package is available on NuGet
PM> install-package SmtpServerStarting a basic SMTP server requires only a few lines of code:
var options = new SmtpServerOptionsBuilder()
.ServerName("localhost")
.Port(25, 587)
.Build();
var smtpServer = new SmtpServer.SmtpServer(options, ServiceProvider.Default);
await smtpServer.StartAsync(CancellationToken.None);There are three hooks that can be implemented; IMessageStore, IMailboxFilter, and IUserAuthenticator.
var options = new SmtpServerOptionsBuilder()
.ServerName("localhost")
.Endpoint(builder =>
builder
.Port(9025, true)
.AllowUnsecureAuthentication(false)
.Certificate(CreateCertificate()))
.Build();
var serviceProvider = new ServiceProvider();
serviceProvider.Add(new SampleMessageStore());
serviceProvider.Add(new SampleMailboxFilter());
serviceProvider.Add(new SampleUserAuthenticator());
var smtpServer = new SmtpServer.SmtpServer(options, serviceProvider);
await smtpServer.StartAsync(CancellationToken.None);
// to create an X509Certificate for testing you need to run MAKECERT.EXE and then PVK2PFX.EXE
// http://www.digitallycreated.net/Blog/38/using-makecert-to-create-certificates-for-development
static X509Certificate2 CreateCertificate()
{
var certificate = File.ReadAllBytes(@"Certificate.pfx");
return new X509Certificate2(certificate, "P@ssw0rd");
}public class SampleMessageStore : MessageStore
{
public override async Task<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 MimeKit.MimeMessage.LoadAsync(stream, cancellationToken);
Console.WriteLine(message.TextBody);
return SmtpResponse.Ok;
}
}public class SampleMailboxFilter : IMailboxFilter, IMailboxFilterFactory
{
public Task<MailboxFilterResult> CanAcceptFromAsync(ISessionContext context, IMailbox @from, int size, CancellationToken cancellationToken)
{
if (String.Equals(@from.Host, "test.com"))
{
return Task.FromResult(MailboxFilterResult.Yes);
}
return Task.FromResult(MailboxFilterResult.NoPermanently);
}
public Task<MailboxFilterResult> CanDeliverToAsync(ISessionContext context, IMailbox to, IMailbox @from, CancellationToken token)
{
return Task.FromResult(MailboxFilterResult.Yes);
}
public IMailboxFilter CreateInstance(ISessionContext context)
{
return new SampleMailboxFilter();
}
}public class SampleUserAuthenticator : IUserAuthenticator, IUserAuthenticatorFactory
{
public Task<bool> AuthenticateAsync(ISessionContext context, string user, string password, CancellationToken token)
{
Console.WriteLine("User={0} Password={1}", user, password);
return Task.FromResult(user.Length > 4);
}
public IUserAuthenticator CreateInstance(ISessionContext context)
{
return new SampleUserAuthenticator();
}
}