Peter Bromberg's .NET Blog All Things Programming

Many developers have difficulty sending mail through Gmail because of security issues. Google provides what is called an "app-specific password" that can be used if you have 2-factor authentication turned on (you should!).

Here is the URL to set this up: https://myaccount.google.com/apppasswords  And here is some sample C# code to use it. You simply replace your regular gmai password with the app-specific password that you set up in your Google settings.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Mail;
using System.Text;
using System.Threading.Tasks;

namespace SendMail
{
class Program
{
static string smtpAddress = "smtp.gmail.com";
static int portNumber = 587;
static bool enableSSL = true;

static string emailFromAddress = "youremail@gmail.com"; //Sender Email Address
static string password = "APPSPECIFICPWD"; //APP SPECIFIC PWD Generated at Google Account
static string emailToAddress = "you@gmail.com"; //Receiver Email Address
static string subject = "Hello";
static string body = "Hello, This is Email sending test using gmail.";

static void Main(string[] args)
{
SendEmail();

}

public static void SendEmail()
{
using (MailMessage mail = new MailMessage())
{
mail.From = new MailAddress(emailFromAddress);
mail.To.Add(emailToAddress);
mail.Subject = subject;
mail.Body = body;
mail.IsBodyHtml = true;
// mail.Attachments.Add(new Attachment("C:\\Temp\\TestFile.txt"));//--Uncomment this to send any attachment

using (SmtpClient smtp = new SmtpClient(smtpAddress, portNumber))
{
smtp.Credentials = new NetworkCredential(emailFromAddress, password);
smtp.EnableSsl = enableSSL;
smtp.Send(mail);
}
}
}

}
}