Testing SMTP with .net

There's also Papercut which is an SMTP server which will receive messages but not deliver them anywhere (allowing you to make sure they are being sent correctly). The received messages are visible in a small GUI and are also written to a directory.

In .NET, SmtpClient can be configured to send email by placing it in a pickup directory.

The default constructor of SmtpClient takes its settings from app.config, so for a test environment we can configure it as follows.

<configuration>
    <system.net>
        <mailSettings>
            <smtp deliveryMethod="specifiedPickupDirectory">
                <specifiedPickupDirectory pickupDirectoryLocation="path to a directory" />
            </smtp>
        </mailSettings>
    </system.net>
</configuration>

MSDN reference - app.config mailSettings element http://msdn.microsoft.com/en-us/library/w355a94k.aspx

For .NET guys out there. Keeping it simple.

We were looking into this and then one of the developers remembered about a the config setting that allows you to override how the emails are sent.

This will create a file per email and leave it alone.

<system.net>
    <mailSettings>
      <smtp deliveryMethod="SpecifiedPickupDirectory">
        <specifiedPickupDirectory pickupDirectoryLocation="\\SharedFolder\MailDrop\" />
      </smtp>      
    </mailSettings>
  </system.net>

I think the blog post A Simple SMTP Server Mock for .NET gives you what you need: a SMTP server mock

A SMTP server mock is basically a fake SMTP server which can be used for unit testing of applications which send email messages.

Also, a google search for smtp mock server will provide you with a selection of SMTP servers for testing purposes. Like:

• Dumbster - Java fake SMTP server
• netDumbster - .NET port of Dumbster

An alternative way to do this is to create a wrapper around the SmtpClient that implements the same interface. Then inject and use the wrapper in your class. When doing unit testing you can then substitute a mock wrapper that has expectations for the method calls and responses.

EDIT: The wrapper is needed (for RhinoMocks, at least) because SmtpClient doesn't derive from an interface and doesn't have virtual methods. If you use a mocking framework that can mock a class without virtual methods directly, you can skip the wrapper and inject the SmtpClient mock directly.

public class SmtpClientWrapper
{
    private SmtpClient Client { get; set; }

    public SmtpClientWrapper( SmtpClient client )
    {
         this.Client = client;
    }

    public virtual void Send( MailMessage msg )
    {
         this.Client.Send( msg );
    }

    ...
}


public class MyClass
{
    private SmtpClientWrapper Client { get; set; }

    public MyClass( SmtpClientWrapper client )
    {
         this.Client = client;
    }

    public void DoSomethingAndNotify()
    {
         ...
         this.Client.Send( msg );
    }
}

Tested (with RhinoMocks) as:

public void DoSomethingAndNotifySendsAMessageTest()
{
     SmtpClientWrapper client = MockRepository.GenerateMock<SmtpClientWrapper>();
     client.Expect( c => c.Send( new MailMessage() ) ).IgnoreArguments();

     MyClass klass = new MyClass( client );

     klass.DoSomethingAndNotify();

     client.VerifyAllExpectations();
}

If you are on Mac OS X you can use MockSMTP.app

You can use Mailnest.io as it is an affordable and yet very effective tool for email testing. It also has a free forever plan for limited usage.