See https://ithoughthecamewithyou.com/post/sending-email-via-gmail-in-cnet-using-smtpclient

GmailSmtpClient.cs

using (SmtpClient smtp = new SmtpClient())
{
    smtp.DeliveryMethod = SmtpDeliveryMethod.Network;
    smtp.UseDefaultCredentials = false;
    smtp.EnableSsl = true;
    smtp.Host = "smtp.gmail.com";
    smtp.Port = 587; 
    smtp.Credentials = new NetworkCredential("email@gmail.com", "password");
    // send the email
}