We can easily mail to designated SMTP Server
using system.web.Mail Namespace,

See the below examble,

// Create mail message
   MailMessage email = new MailMessage();
   // Set message parameters
   email.From = txtFrom.Text;
   email.To = txtRecipient.Text;
   email.Subject = txtSubject.Text;
   email.BodyFormat = System.Web.Mail.MailFormat.Text;
   email.Body = txtMessage.Text;
   // Add attachment
   if(txtMessage.Text != “”)
       email.Attachments.Add(new MailAttachment(txtAttachment.Text,
                                              MailEncoding.Base64));
   // Set SMTP server
   SmtpMail.SmtpServer = txtSmtpServer.Text;
   // Now send message
   SmtpMail.Send(email);

Hope this helps,

Happy Coding.