See https://ithoughthecamewithyou.com/post/sending-email-via-gmail-in-cnet-using-smtpclient#a601bc7c782944268c8be78a4e007b29

GmailSmtp.cs

// Gmail Address from where you send the mail 
var fromAddress = "username@gmail.com";
// any address where the email will be sending 
var toAddress = YourEmail.Text.ToString();
//Password of your gmail address 
const string fromPassword = "pass";
// Passing the values and make a email formate to display 
string subject = YourSubject.Text.ToString();
string body = "From: " + YourName.Text + "\n";
body += "Email: " + YourEmail.Text + "\n"; 
body += "Subject: " + YourSubject.Text + "\n"; 
body += "Question: \n" + Comments.Text + "\n"; 
// smtp settings 
var smtp = new System.Net.Mail.SmtpClient(); 
{ 
    smtp.Host = "smtp.gmail.com"; 
    smtp.Port = 587; smtp.EnableSsl = true; 
    smtp.DeliveryMethod = System.Net.Mail.SmtpDeliveryMethod.Network; 
    smtp.Credentials = new NetworkCredential(fromAddress, fromPassword);
    smtp.Timeout = 20000; 
} 
// Passing values to smtp object smtp.Send(fromAddress, toAddress, subject, body);