如何根据新的安全策略在 .Net 中发送电子邮件

一般解决方案是 https://galleryserverpro.com/use-gmail-as-your-smtp-server-even-when-using-2-factor-authentication-2-step-verification/

1）使用浏览器登录您的Google帐户，然后转到您的登录和安全设置。查找两步验证设置。

2）如果两步验证已关闭，并且您希望保持这种方式，这意味着您将需要实现您所说的许多身份验证机制。

解决方案：将其打开，然后生成并使用Google应用密码。它应该有效！您不需要使用其他库，例如 mailkit .

如何获取用户OAuthToken？

您需要做的第一件事是按照 Google 的说明为您的应用程序获取 OAuth 2.0 凭据。

完成此操作后，获取访问令牌的最简单方法是使用Google的Google.Apis.Auth库：

using System;
using System.Threading;
using System.Security.Cryptography.X509Certificates;
using Google.Apis.Auth.OAuth2;
using MimeKit;
using MailKit.Net.Smtp;
using MailKit.Security;
namespace Example {
    class Program
    {
        public static async void Main (string[] args)
        {
            var certificate = new X509Certificate2 (@"C:'path'to'certificate.p12", "password", X509KeyStorageFlags.Exportable);
            var credential = new ServiceAccountCredential (new ServiceAccountCredential
                .Initializer ("your-developer-id@developer.gserviceaccount.com") {
                    // Note: other scopes can be found here: https://developers.google.com/gmail/api/auth/scopes
                    Scopes = new[] { "https://mail.google.com/" },
                    User = "username@gmail.com"
                }.FromCertificate (certificate));
            // Note: result will be true if the access token was received successfully
            bool result = await credential.RequestAccessTokenAsync (CancellationToken.None);
            if (!result) {
                Console.WriteLine ("Error fetching access token!");
                return;
            }
            var message = new MimeMessage ();
            message.From.Add (new MailboxAddress ("Your Name", "username@gmail.com"));
            message.To.Add (new MailboxAddress ("Recipient's Name", "recipient@yahoo.com"));
            message.Subject = "This is a test message";
            var builder = new BodyBuilder ();
            builder.TextBody = "This is the body of the message.";
            builder.Attachments.Add (@"C:'path'to'attachment");
            message.Body = builder.ToMessageBody ();
            using (var client = new SmtpClient ()) {
                client.Connect ("smtp.gmail.com", 587, SecureSocketOptions.StartTls);
                // use the access token as the password string
                client.Authenticate ("username@gmail.com", credential.Token.AccessToken);
                client.Send (message);
                client.Disconnect (true);
            }
        }
    }
}

使用 Google.Apis.Auth.OAuth2 是最佳实践技术吗？

为什么不使用他们的 API 来获取身份验证令牌？这似乎是最好的方法，把它交给我...

我可以向其他非 Gmail 帐户发送电子邮件吗？

是的，您通过GMail发送的任何电子邮件都可以发送到任何其他电子邮件地址 - 它不必只发送到其他GMail地址。

未实施 Google 特定安全要求的应用中使用 Gmail SMTP 服务器时，会发生身份验证错误。在 Gmail 帐号设置中，开启： "登录和安全"> "关联的应用和网站"> "允许安全性较低的应用"> 上

using System;
using System.Net;
using System.Net.Mail;
using System.Net.Mime;
using System.Threading;
using System.ComponentModel;
namespace Examples.SmtpExamples.Async
{
public class SimpleAsynchronousExample
{
    static bool mailSent = false;
    private static void SendCompletedCallback(object sender, AsyncCompletedEventArgs e)
    {
        // Get the unique identifier for this asynchronous operation.
         String token = (string) e.UserState;
        if (e.Cancelled)
        {
             Console.WriteLine("[{0}] Send canceled.", token);
        }
        if (e.Error != null)
        {
             Console.WriteLine("[{0}] {1}", token, e.Error.ToString());
        } else
        {
            Console.WriteLine("Message sent.");
        }
        mailSent = true;
    }
    public static void Main(string[] args)
    {
        // Command-line argument must be the SMTP host.
        SmtpClient client = new SmtpClient(args[0]);
        // Specify the email sender.
        // Create a mailing address that includes a UTF8 character
        // in the display name.
        MailAddress from = new MailAddress("jane@contoso.com",
           "Jane " + (char)0xD8+ " Clayton",
        System.Text.Encoding.UTF8);
        // Set destinations for the email message.
        MailAddress to = new MailAddress("ben@contoso.com");
        // Specify the message content.
        MailMessage message = new MailMessage(from, to);
        message.Body = "This is a test email message sent by an application. ";
        // Include some non-ASCII characters in body and subject.
        string someArrows = new string(new char[] {''u2190', ''u2191', ''u2192', ''u2193'});
        message.Body += Environment.NewLine + someArrows;
        message.BodyEncoding =  System.Text.Encoding.UTF8;
        message.Subject = "test message 1" + someArrows;
        message.SubjectEncoding = System.Text.Encoding.UTF8;
        // Set the method that is called back when the send operation ends.
        client.SendCompleted += new
        SendCompletedEventHandler(SendCompletedCallback);
        // The userState can be any object that allows your callback
        // method to identify this send operation.
        // For this example, the userToken is a string constant.
        string userState = "test message1";
        client.SendAsync(message, userState);
        Console.WriteLine("Sending message... press c to cancel mail. Press any other key to exit.");
        string answer = Console.ReadLine();
        // If the user canceled the send, and mail hasn't been sent yet,
        // then cancel the pending operation.
        if (answer.StartsWith("c") && mailSent == false)
        {
            client.SendAsyncCancel();
        }
        // Clean up.
        message.Dispose();
        Console.WriteLine("Goodbye.");
    }
}