If you ever have the need to send mail through a GMail account, this sample may save you a few minutes. It isn't hard, but there are a few differences which require SSL and authentication.
//-- Establish Locals
SmtpClient smtp = new SmtpClient("smtp.gmail.com ", 587);
MailMessage msg = new MailMessage("reply@somewhere.com", "to@somewhere.com");
//-- Set the subject line
msg.Subject = "Hello World";
//-- Set the body (Plain text in this sample)
msg.Body = "Here is the body of the message.";
//-- Attach the file if necessary
msg.Attachments.Add(new Attachment(pathAndFileName));
smtp.EnableSsl = true;
smtp.DeliveryMethod = SmtpDeliveryMethod.Network;
smtp.UseDefaultCredentials = false;
smtp.Credentials = new NetworkCredential("myemail@gmail.com", "mypassword");
//-- Send the message
smtp.Send(msg);