身份验证错误发送 SMTP 请求

Question

我正在编写一个 C# 电子邮件应用程序，该应用程序目前设计用于 Gmail，因此我可以测试身份验证。但是，我收到一个似乎没有多大意义的错误，因为我将 SSL 设置为 true 并使用用户和密码。

错误信息： System.Net.Mail.SmtpException: 'The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required. Learn more at'

using System;
using System.Net;
using System.Net.Mail;

namespace EmailSendingProgram
{
    public class EmailSendingClass
    {
        public static void Main(string[] args)
        {
            Console.WriteLine("Type your Gmail Address: ");
            string from = Console.ReadLine();

            Console.WriteLine("Type your Gmail Password: ");
            string password = Console.ReadLine();

            Console.WriteLine("Type the Email Address you wish to send to: ");
            string to = Console.ReadLine();

            Console.WriteLine("Type the Subject of the email: ");
            string subject = Console.ReadLine();

            Console.WriteLine("Type or paste in your email (either text or HTML): ");
            string body = Console.ReadLine();

            EmailSendingClass email = new EmailSendingClass();
            email.Send(from, password, to, subject, body);
        }

        /// handles sending the email
        /// hardcoded to work with gmail just change the CreateSmtpClient from 
        /// "smtp.gmail.com", 587 to whatever you want to use
        public void Send(string from, string password, string to, string subject, string body)
        { 
            var message = CreateMailMessage(from, to, subject, body);

            // Host and Port setup for use with Gmail
            using (SmtpClient client = CreateSmtpClient("smtp.gmail.com", 587, from, password))
            {
                client.Send(message);
            }
        }

        /// Defines the SmtpClient for the mail message 
        /// setups up the network credentials to send the email
        private SmtpClient CreateSmtpClient(string host, int port, string from, string password)
        {
            SmtpClient client = null;

            client = new SmtpClient()
            {
                Host = host,
                Port = port,
                EnableSsl = true,
                Credentials = new NetworkCredential(from, password)
            };

            return client;
        }

        /// defines what is contained in the email and where it will be sent
        /// also makes all messages send as HTML
        private MailMessage CreateMailMessage(string from, string to, string subject, string body)
        {
            MailMessage message = null;

            message = new MailMessage(from, to)
            {
                Subject = subject,
                Body = body
            };

            message.IsBodyHtml = true;
            return message;
        }
    }
}

我知道身份验证有误，但我似乎无法弄清楚具体是什么。因此，我们将不胜感激。

Answer 1

我遇到了由 TLS 1.2 支持问题引起的类似问题。如果是这种情况，最简单的解决方案可能是面向 .NET 4.6.1 或更高版本。可以找到其他建议 here and here.

Answer 2

问题不是程序，而是 Gmail 拒绝从 "less secure apps"

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身份验证错误发送 SMTP 请求

Authentication error sending SMTP Request

.net

c#

email

authentication

smtpclient