到2017年3月，这对我来说是有效的。 从上面的解决方案开始:“终于开始工作了:)”，一开始并没有工作。

SmtpClient client = new SmtpClient();
client.Port =  587;
client.Host = "smtp.gmail.com";
client.EnableSsl = true;
client.Timeout = 10000;
client.DeliveryMethod = SmtpDeliveryMethod.Network;
client.UseDefaultCredentials = false;
client.Credentials = new System.Net.NetworkCredential("<me>@gmail.com", "<my pw>");
MailMessage mm = new MailMessage(from_addr_text, to_addr_text, msg_subject, msg_body);
mm.BodyEncoding = UTF8Encoding.UTF8;
mm.DeliveryNotificationOptions = DeliveryNotificationOptions.OnFailure;

client.Send(mm);

如果你想让你的电子邮件和密码不出现在你的代码，并希望你的公司电子邮件客户端服务器使用你的windows凭据使用下面。

client.Credentials = CredentialCache.DefaultNetworkCredentials;

源

 //Hope you find it useful, it contain too many things

    string smtpAddress = "smtp.xyz.com";
    int portNumber = 587;
    bool enableSSL = true;
    string m_userName = "support@xyz.com";
    string m_UserpassWord = "56436578";

    public void SendEmail(Customer _customers)
    {
        string emailID = gghdgfh@gmail.com;
        string userName = DemoUser;

        string emailFrom = "qwerty@gmail.com";
        string password = "qwerty";
        string emailTo = emailID;

        // Here you can put subject of the mail
        string subject = "Registration";
        // Body of the mail
        string body = "<div style='border: medium solid grey; width: 500px; height: 266px;font-family: arial,sans-serif; font-size: 17px;'>";
        body += "<h3 style='background-color: blueviolet; margin-top:0px;'>Aspen Reporting Tool</h3>";
        body += "<br />";
        body += "Dear " + userName + ",";
        body += "<br />";
        body += "<p>";
        body += "Thank you for registering </p>";            
        body += "<p><a href='"+ sURL +"'>Click Here</a>To finalize the registration process</p>";
        body += " <br />";
        body += "Thanks,";
        body += "<br />";
        body += "<b>The Team</b>";
        body += "</div>";
       // this is done using  using System.Net.Mail; & using System.Net; 
        using (MailMessage mail = new MailMessage())
        {
            mail.From = new MailAddress(emailFrom);
            mail.To.Add(emailTo);
            mail.Subject = subject;
            mail.Body = body;
            mail.IsBodyHtml = true;
            // Can set to false, if you are sending pure text.

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

这样的:

mail.To = "user@hotmail.com";

应该是:

mail.To.Add(new MailAddress("user@hotmail.com"));

邮件。寄和寄。From是只读的。将它们移动到构造函数中。

using System.Net.Mail;

...

MailMessage mail = new MailMessage("you@yourcompany.example", "user@hotmail.com");
SmtpClient client = new SmtpClient();
client.Port = 25;
client.DeliveryMethod = SmtpDeliveryMethod.Network;
client.UseDefaultCredentials = false;
client.Host = "smtp.gmail.com";
mail.Subject = "this is a test email.";
mail.Body = "this is my test email body";
client.Send(mail);

这也可以…

string your_id = "your_id@gmail.com";
string your_password = "password";
try
{
   SmtpClient client = new SmtpClient
   {
     Host = "smtp.gmail.com",
     Port = 587,
     EnableSsl = true,
     DeliveryMethod = SmtpDeliveryMethod.Network,
     Credentials = new System.Net.NetworkCredential(your_id, your_password),
     Timeout = 10000,
   };
   MailMessage mm = new MailMessage(your_iD, "recepient@gmail.com", "subject", "body");
   client.Send(mm);
   Console.WriteLine("Email Sent");
 }
 catch (Exception e)
 {
   Console.WriteLine("Could not end email\n\n"+e.ToString());
 }