Exchange Web Services API: Error Sending Message with Attachment

Question

I am attempting to send a message with a PDF attachment using the EWS Managed API 2.0. I am sending email as an account that is not my own but for which I have send as permissions.

I can send the email without an attachment, but as soon as I try to send the attachment the request fails.

The file definitely exists.

I have implemented the TraceListener and see that the Create Attachment request is sent when SendAndSaveCopy is called but I do not receive a proper response from the server (I do know the server is getting my request though as the error is clearly from the server). I do not see a request to send the email message after the create attachment appears to fail.

The error I receive upon trying to SendAndSaveCopy is The request failed. The underlying connection was closed: An unexpected error occurred on a send. The inner exception is Unable to write data to the transport connection: An existing connection was forcibly closed by the remote host.

I have googled this and according to what few suggestions I've found, I've confirmed this is not simply a timeout of the subscription (supported by the fact in the exact same context I can SendAndSaveCopy just fine without an attachment, and also by the fact I can send an error email after the failure just fine). Others have cited issues with file size, but my file size is very small (151 KB).

My Exchange administrator is checking to see if there is a setting on the server side that could be affecting this but hasn't found anything yet.

Can anyone tell me if they have encountered (and found a resolution to) this particular problem? Even any tips about the particular settings I could direct my Exchange administrator to look at?

My code is attached below (I've removed my gobs of error message printing for readability):

Public Function SendEmailResponse(ByVal strSender As String, ByVal strRecipient As String, ByVal strSubject As String, ByVal strBody As String, _
                        ByVal ews2010 As ExchangeService, Optional ByVal strCCAddresses As List(Of String) = Nothing, _
                        Optional ByVal strFilesToAttach As List(Of String) = Nothing, _
                        Optional ByVal blnReceipt As Boolean = False) As Boolean
    Try
        Dim msgReply As New EmailMessage(ews2010)
        msgReply.Subject = strSubject
        msgReply.Body = New MessageBody(BodyType.Text, strBody)
        Dim fromAddress As New EmailAddress(strSender)
        msgReply.From = fromAddress
        msgReply.ToRecipients.Add(strRecipient)
        msgReply.IsReadReceiptRequested = blnReceipt
        If strCCAddresses IsNot Nothing Then
            For Each strCC As String In strCCAddresses
                msgReply.CcRecipients.Add(strCC)
            Next
        End If
        msgReply.Save()  '''This works just fine

        If strFilesToAttach IsNot Nothing Then
            For Each flAttach In strFilesToAttach
                msgReply.Attachments.AddFileAttachment(flAttach)
            Next
        End If
        msgReply.SendAndSaveCopy() '''CRASHES HERE IF AND ONLY IF I've attached files in the above loop
        SendEmailResponse = True
    Catch ex As Exception
        SendEmailResponse = False
    End Try
End Function

Update: my Exchange administrator has tracked down the problem to the load balancer somehow. If I connect directly to the exchange server the problem vanishes; but the autodiscoverurl connects to the load balancer. He's following up on that now. Hopefully I'll have a complete solution up soon, but thought I'd go ahead and post in case this gives anyone any ideas or in case it helps someone else... — R Zeckoski, May 29 '13 at 19:45

score 0 · Answer 1 · edited May 23 '17 at 12:16

From the OP:

My Exchange administrator has tracked down the problem to the load balancer somehow. If I connect directly to the exchange server the problem vanishes; but the autodiscoverurl connects to the load balancer. He's following up on that now. Hopefully I'll have a complete solution up soon, but thought I'd go ahead and post in case this gives anyone any ideas or in case it helps someone else.

score 0 · Answer 2 · answered Jan 16 '14 at 15:35

We were at this for months and I don't think we ever arrived at the 'proper' solution to this. We tracked it down to the Application Security Manager enabled on a Virtual IP Address on F5. It was scanning the traffic and deeming the attachments unsafe.

Exchange Web Services API: Error Sending Message with Attachment

2 Answers2