smtp clients `SendAsync()` method

Question

 Protected Sub btnLocalSubmit_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnLocalSubmit.Click
            Dim logic = New connections
            logic.emailsToSend(User.Identity.Name, getURL, reportedBy)
            SendAsync()
            Response.Redirect(getRedirectionPath, False)
        Catch ex As Exception
            Response.Write(ex.Message)
        Finally
            _con.Close()
            _con.Dispose()
            _sqlComm.Dispose()
        End Try
    End Sub
    Sub SendAsync()
        Dim _con As New SqlConnection(ConfigurationManager.ConnectionStrings("CitizenJDBConnectionString").ConnectionString)
        Dim _sqlDataAdapter As New SqlDataAdapter("SELECT * FROM EmailSender", _con)
        Dim _table As New System.Data.DataTable
        Try
            _con.Open()
            _sqlDataAdapter.Fill(_table)
            _con.Close()
            For i As Integer = 0 To _table.Rows.Count - 1

                Dim AppPath As String = Request.PhysicalApplicationPath
                Dim sr As New StreamReader(AppPath & "EmailTemplates/NewReport.txt")
                Dim message As New MailMessage()
                message.IsBodyHtml = True
                message.From = New MailAddress("[e-mail]")
                message.To.Add(New MailAddress(_table.Rows(i).Item(1)))

                message.Subject = "New User registration !"
                message.Body = sr.ReadToEnd()
                sr.Close()
                message.Body = message.Body.Replace("<%ReporterName%>", _table.Rows(i).Item(3))
                message.Body = message.Body.Replace("<%ReportURL%>", _table.Rows(i).Item(2))
                Dim client As New SmtpClient()
                client.Host = "smtp.xxxxx.com"
                'smtp.gmail.com
                client.Port = 25
                client.UseDefaultCredentials = True
                client.Credentials = New System.Net.NetworkCredential("[e-mail]", "123456")
                'client.EnableSsl = True
                Dim userState As Object = message
                'wire up the event for when the Async send is completed
                AddHandler client.SendCompleted, AddressOf SmtpClient_OnCompleted
                client.SendAsync(message, userState)
            Next
        Catch ex As Exception
            Response.Write(ex.Message)
        End Try

    End Sub 'SendAsync
    Public Sub SmtpClient_OnCompleted(ByVal sender As Object, ByVal e As AsyncCompletedEventArgs)
        'Get the Original MailMessage object
        Dim message As MailMessage = CType(e.UserState, MailMessage)
        'write out the subject
        Dim subject As String = message.Subject
        If e.Cancelled Then
            Console.WriteLine("Send canceled for mail with subject [{0}].", subject)
        End If
        If Not (e.Error Is Nothing) Then
            Console.WriteLine("Error {1} occurred when sending mail [{0}] ", subject, e.Error.ToString())
        Else
            Console.WriteLine("Message [{0}] sent.", subject)
        End If
    End Sub 'SmtpClient_OnCompleted

我正在使用 smtp 客户端SendAsync()功能异步发送电子邮件......但是此功能不起作用...为什么？？我没有收到任何电子邮件。当我同步发送它时...我收到电子邮件，这意味着我的设置是正确的...那么SendAsync()方法有什么问题呢？

Answer 1

我一直这样做，经过多年的努力，我建议为您的问题提供 (2( 折解决方案：

1. 将实际发送电子邮件代码(System.Net 内容(重构为 WCF 服务或单独的.dll(我更喜欢该服务(。
2. 继续使用 ASP.NET 页面中的异步委托调用，但以"即发即弃"的方式执行此操作，不要连接任何回调。

您可能会说您需要知道发送电子邮件时是否出了问题。让发送电子邮件的 WCF 服务处理此问题。在服务中进行任何日志记录。毕竟，无论如何，您真正要做的就是伐木。如果您需要在电子邮件失败时对工作流程进行更高级的处理，可以通过多种方式标记您的 ASP.NET，但我认为您会发现，一旦发送电子邮件的服务稳定，您将很少遇到问题。

事实上，多年来我一直在使用 ASP.NET 调用的服务来发送电子邮件，并且已经发送了数千封不同电子邮件中的 10 封，并且这种即发即弃的设计从未遇到任何问题。

最后，设置页面Async=True使页面最终通过阻塞主线程直到所有异步进程完成来整体同步运行。这会使页面加载速度非常慢，并且通常不需要。