Getting Error while sending the email in .NET

Question

I have an application was working fine and all the email functionality was working fine.

From yesterday, I started getting below error

Error Message:Service not available, closing transmission channel. The server response was: 4.3.2 Service not available, closing transmission channel

My VB.net code for sendmail is given below:

 Public Sub SendMessage(ByVal toAddress As String, ByVal ccAddress As String)
        Try
            Dim message As New MailMessage()
            Dim client As New SmtpClient()
            'Set the sender's address
            message.From = New MailAddress(fromAddress)
            If (toAddress.Trim.Length > 0) Then
                For Each addr As String In toAddress.Split(";"c)
                    message.To.Add(New MailAddress(addr))
                Next
            End If
            If (ccAddress.Trim.Length > 0) Then
                For Each addr As String In ccAddress.Split(";"c)
                    message.CC.Add(New MailAddress(addr))
                Next
            End If
            message.BodyEncoding = Encoding.UTF8
            message.Subject = Subject
            message.Body = Body
            message.IsBodyHtml = True
            client.Send(message)
        Catch ex As Exception
            ErrorHandler.WriteError(ex.Message)
        End Try
    End Sub

Please suggest what can be cause behind this error and do let me know how can I fix this issue.

Answer 1

Hi, There isn't anything wrong with your code. This part of the error message:

4.3.2 Service not available, closing transmission channel

Is actually coming from your mail server, and the framework is simply passing the error message on to your application, and throwing it as part of the exception.

4.x.x errors are usually temporary, and are meant to be retried. Typically mail servers are overloaded when they throw a 400 error.

Cheers!

Dave

Answer 2

Check your email and see if it starts working.

Instead of (or in addition to) smtp authentication, some email servers will allow mail to be sent for 30 minutes (or some length) after a client computer checks POP email. If this is the case, it can make an application that does not use smtp authentication appear work sometimes and not work sometimes, with no change in the code.