asp.net - smtp客户端 `SendAsync()`方法

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("admin@xxxx.com")

                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("admin@xxxx.com", "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() 函数异步发送电子邮件...但是这个函数不起作用...为什么？我没有收到任何电子邮件..当我同步发送时...我收到了电子邮件，这意味着我的设置是正确的...那么 SendAsync() 方法有什么问题？

Answer 1

我一直这样做，经过多年这样做，我建议对您的问题采用 (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. 继续从 ASP.NET 页面使用异步委托(delegate)调用，但以“即发即忘”的方式执行此操作，无需连接任何回调。

您可能会说您需要知道发送电子邮件时是否出现问题。让发送电子邮件的 WCF 服务来处理此问题。在服务中进行任何日志记录。毕竟你真正做的就是记录。如果您需要在电子邮件失败时更好地处理工作流程，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，多年来我一直使用 ASP.NET 调用的服务来发送电子邮件，并且已经发送了数以万计的不同电子邮件，并且这种即发即忘的设计从未遇到过任何问题。

最后，设置页面 Async=True 通过阻塞主线程直到所有异步进程完成，最终使页面整体同步运行。这可能会使页面加载速度非常慢，通常是不需要的。