Something like this should work:
Dim Smtp_Client As New SmtpClient
Smtp_Client.DeliveryMethod = SmtpDeliveryMethod.SpecifiedPickupDirectory
Smtp_Client.PickupDirectoryLocation = "C:\temp\"
Dim eMail As New MailMessage
...
Smtp_Client.Send(eMail)
The message will be saved in the specified directory as an
.eml
file, which you can open with Outlook.