Welcome to SMTP.WS

Where is my SMTP server on Vista?  I'm not sure why more developers haven't asked this question. 
Simple, it is not included - http://blogs.iis.net/bills/archive/2006/09/18/IIS7-_2D00_-Vista-vs.-Longhorn-Server.aspx

Here are a couple I've used on Vista Ultimate.   I'm sure there are others but for testing, SMTP is additional 'feature' you'll need to add, at this point. 

Free SMTP Server (This is handy, runs as an app and simple to configure for testing your apps).
http://softstack.com/freesmtp.html

Smartermail - Free for one domain.
http://www.smartertools.com/Products/SmarterMail/Free.aspx

Steve Schofield
Microsoft MVP - IIS

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Some additional testing. 
In IIS7 SMTP properties, if you put a smarthost or server that allows relaying.  This will work too for testing.  Then you won't have to install anything on Vista.

Here is the code I used to send email to a smarthost on Vista.

        'create the mail message
        Dim mail As New System.Net.Mail.MailMessage()

        'set the addresses
        mail.From = New Net.Mail.MailAddress("me@mycompany.com")
        mail.To.Add("Steve@ChangeThisToSomething.com")

        'set the content
        mail.Subject = "This is an email"
        mail.Body = "this is a sample body"

        'send the message
        Dim smtp As New Net.Mail.SmtpClient()
        smtp.Send(mail)

Here is the picture of my settings on Vista to send email to a remote relay.