SmtpServer is a simple, but highly functional SMTP server implementation. Written entirely in C# it takes full advantage of the .NET TPL to achieve maximum performance.
SmtpServer is available via NuGet https://www.nuget.org/packages/SmtpServer/
SmtpServer currently supports the following ESMTP extensions:
- STARTTLS
- SIZE
- PIPELINING
- 8BITMIME
- AUTH PLAIN LOGIN
At its most basic, it only takes a few lines of code for the server to be listening to incoming requests.
var options = new OptionsBuilder()
.ServerName("localhost")
.Port(25, 587)
.Build();
var smtpServer = new SmtpServer.SmtpServer(options);
await smtpServer.StartAsync(CancellationToken.None);There are three hooks that can be implemented; IMessageStore, IMailboxFilter, and IUserAuthenticator.
var options = new OptionsBuilder()
.ServerName("localhost")
.Port(25, 587)
.MessageStore(new SampleMessageStore())
.MailboxFilter(new SampleMailboxFilter())
.UserAuthenticator(new SampleUserAuthenticator())
.Build();
var smtpServer = new SmtpServer.SmtpServer(options);
await smtpServer.StartAsync(CancellationToken.None);public class SampleMessageStore : MessageStore
{
public Task<SmtpResponse> SaveAsync(ISessionContext context, IMessageTransaction transaction, CancellationToken cancellationToken)
{
var textMessage = (ITextMessage)transaction.Message;
var message = MimeKit.MimeMessage.Load(textMessage.Content);
Console.WriteLine(message.TextBody);
return Task.FromResult(SmtpResponse.Ok);
}
}public class SampleMailboxFilter : IMailboxFilter
{
public Task<MailboxFilterResult> CanAcceptFromAsync(ISessionContext context, IMailbox @from, int size = 0)
{
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)
{
return Task.FromResult(MailboxFilterResult.Yes);
}
}public class SampleUserAuthenticator : IUserAuthenticator
{
public Task<bool> AuthenticateAsync(string user, string password)
{
Console.WriteLine("User={0} Password={1}", user, password);
return Task.FromResult(user.Length > 4);
}
}