I’m trying to attach a file to an e-mail that I’m sending using the SmtpClient class (from System.Net.Mail) using C# for ASP.NET. Everything works correctly, but the problem is that the file that was uploaded gets locked in the folder by Windows and I can’t delete it afterwards.
This is the code I used to attach a file to an e-mail:

sHtmlConfirmation = "D:\\ftpsite\\from_web\\" + sFolder + "\\" + sFolder + ".htm";
Attachment data = new Attachment (sHtmlConfirmation);
Email.Attachments.Add (data);

I needed a solution to prevent Windows from locking a file that it uses, so I turned to the MSDN Forums for help. James Curran posted a working solution. He suggested employing the using statement to dispose the MailMessage object after the mail has been sent.
The code which fixes the problem is:

using (MailMessage Email = new MailMessage ())
{
// setup message details here
}

After the mail was sent, I was able to move the folder where the attached file was used.