Something like:
// Read the file
string body = File.ReadAllText(@"C:\\MyPath\\file.txt");
MailMessage mail = new MailMessage("you@you.com", "them@them.com");
SmtpClient client = new SmtpClient();
client.Port = 25;
client.DeliveryMethod = SmtpDeliveryMethod.Network;
client.UseDefaultCredentials = false;
client.Host = "smtp.google.com";
mail.Subject = "file";
// Set the read file as the body of the message
mail.Body = body;
// Send the email
client.Send(mail);