I am currently using Process.Start to send simple emails from my WinForms app. Can you think of any way to add a file attachment to the email? (Edit: using Process.Start?)
Try something like this -->
MailMessage theMailMessage = new MailMessage("from@email.com", "to@email.com");
theMailMessage.Body = "body email message here";
theMailMessage.Attachments.Add(new Attachment("pathToEmailAttachment"));
theMailMessage.Subject = "Subject here";
SmtpClient theClient = new SmtpClient("IP.Address.Of.Smtp");
theClient.UseDefaultCredentials = false;
System.Net.NetworkCredential theCredential = new System.Net.NetworkCredential("user@name.com", "password");
theClient.Credentials = theCredential;
theClient.Send(theMailMessage);
Alright, based on your edit and additional info, I found this Blog Post by Jon Galloway, "Sending files via the default e-mail client".
This looks like what you may be looking for, though I don't profess any knowledge with this way as I have always used the method I posted.
Hopefully it is of use to you.