Send email from Gmail account using Goddady
public static bool _SendMail(string tMailTo, string tSubject, string tBody, string tAttach)
{
    MailMessage mail = new MailMessage();
    mail.From = new MailAddress(tMailFrom);
    mail.To.Add(tMailTo);
    mail.Subject = tSubject;
    if (!tAttach.Equals(""))
    {
        mail.Attachments.Add(new Attachment(tAttach));
    }
    mail.Body = tBody;
    mail.IsBodyHtml = true;

    SmtpClient smtp = new SmtpClient();
    smtp.Host = "relay-hosting.secureserver.net";
    smtp.Send(mail);
    return true;
}

smtp.Credentials = new NetworkCredential(smtpUser, smtpPass);
smtp.EnableSsl = true;

<system.net>
<mailSettings>
  <smtp deliveryMethod="Network" from="username@gmail.com">
    <network host="smtp.gmail.com" userName="username@gmail.com" password="password" enableSsl="true" port="587" />
  </smtp>
</mailSettings>