我正在尝试使用SmtpClient.SendMailAsync方法发送大量电子邮件.
这是我从简单的控制台应用程序调用的测试方法.

    static void Main(string[] args)
    {

        SendMailsOnebyOneAsync().GetAwaiter().GetResult();

    }


    public static async Task SendMailsOnebyOneAsync()
    {
        for (int i = 0; i < 1000; i++)
        {
            try
            {
                using (SmtpClient sMail = new SmtpClient("XXX"))
                {
                    sMail.DeliveryMethod = SmtpDeliveryMethod.Network;
                    sMail.UseDefaultCredentials = false;
                    sMail.Credentials = null;

                    var fromMailAddress = new MailAddress("XXX");
                    var toMailAddress = new MailAddress("XXX");

                    MailMessage message = new MailMessage(fromMailAddress, toMailAddress)
                    {
                        Subject = "test"
                    };

                    await sMail.SendMailAsync(message);

                    Console.WriteLine("Sent {0}", i);
                }
            }
            catch (Exception e)
            {
                Console.WriteLine(e.Message);
            }
        }
    }

有时这个方法是悬挂的 – 它等待SendMailAsync,它似乎卡住而且不会返回.

我看到一个相关的问题
SmtpClient SendMailAsync sometimes never returns
但没有任何修复建议对我有用.

当我尝试使用同步方法SmtpClient.Send时一切正常,应用程序永远不会挂起.

有谁知道出了什么问题？

解决方法:

使用一个客户端发送重复的邮件.不断创建和处置许多客户端可能会出现端口问题.

public static async Task SendMailsOnebyOneAsync() {
    using (var sMail = new SmtpClient("XXX")) {
        sMail.DeliveryMethod = SmtpDeliveryMethod.Network;
        sMail.UseDefaultCredentials = false;
        sMail.Credentials = null;

        for (int i = 0; i < 1000; i++) {
            try {
                var fromMailAddress = new MailAddress("XXX");
                var toMailAddress = new MailAddress("XXX");

                var message = new MailMessage(fromMailAddress, toMailAddress) {
                    Subject = "test"
                };

                await sMail.SendMailAsync(message);

                Console.WriteLine("Sent {0}", i);
            } catch (Exception e) {
                Console.WriteLine(e.Message);
            }
        }
    }
}

其次,虽然可能就像这是一个例子,尝试一次发送许多电子邮件是不合理的.