This is a simple C# program that send email to recipient. It uses gmail smtp.

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

namespace SendEmail
{
    class Program
    {
        static void Main(string[] args)
        {
            var fromAddress = new MailAddress("from@gmail.com", "From Name");//Email Address for from Email
            var toAddress = new MailAddress("to@example.com", "To Name");//Recipient address
            const string fromPassword = "fromPassword";//Gmail Password for user
            const string subject = "Subject";//Subject of email
            const string body = "Body";//Body content for email


            var smtp = new SmtpClient
            {
                Host = "smtp.gmail.com",
                Port = 587,
                EnableSsl = true,
                DeliveryMethod = SmtpDeliveryMethod.Network,
                UseDefaultCredentials = false,
                Credentials = new NetworkCredential(fromAddress.Address, fromPassword)//Credentials of gmail user
            };
            using (var message = new MailMessage(fromAddress, toAddress)
            {
                //IsBodyHtml=true,//Set it to true if your email body contains html content
                Subject = subject,
                Body = body
            })
            {
                smtp.Send(message);
            }
        }
    }
}