development smtp server for windows

There are a few:

• SMTP Impostor (formerly Antix SMTP Server), NuGet package - looks very good
• Dumbster - fake SMTP server under Apache license

Or you can also set it up in your web.config to just store the e-mails in the file system (the config way of what "silky" has proposed in code):

<system.net>  
   <mailSettings>  
      <smtp deliveryMethod="SpecifiedPickupDirectory">  
         <specifiedPickupDirectory 
             pickupDirectoryLocation="c:\temp\mails\"/>  
      </smtp>  
   </mailSettings>  
</system.net>  

Marc

I know that this is an old post however I also know about http://smtp4dev.codeplex.com/ which I would also recommend. It sits on you task bar and then pops up when you send emails to it. It allows you to then examine the email in quite some depth.