You can't send large attachments by using the EWS client

Consider the following scenario:
  • A user connects to their mailbox by using an Exchange Web Services (EWS) client.
  • The user's mailbox is located on Site B.
  • The client connection is made to a Microsoft Exchange server on Site A.
  • The Exchange server on Site A proxies the request to an Exchange server on Site B.

In this scenario, the user cannot send an email that includes large attachments. When you use the Outlook for Mac client, it moves the message into the Drafts folder and returns the following error:

An unknown error has occurred. Connection to the server failed or was dropped. Outlook cannot send the message, because the message size exceed the maximum limit set on the server

The EWS logs for Site A show an HTTP 500 status with a generic error that resembles the following:

ReportException_Message=Exchange Web Services are not currently available for this request because none of the Client Access Servers in the destination site could process the request.;ReportException_StackTrace= at Microsoft.Exchange.Services.Wcf.EWSService.GetServiceAsyncResult[TSoapResponseBody](IAsyncResult result) at Microsoft.Exchange.Services.Wcf.EWSService.CreateSoapResponse[TSoapResponse;TSoapResponseBody](IAsyncResult result; Func`2 createSoapResponseCallback) at AsyncInvokeEndEndCreateItem(Object ; Object[] ; IAsyncResult ) at System.ServiceModel.Dispatcher.AsyncMethodInvoker.InvokeEnd(Object instance; Object[]& outputs; IAsyncResult result) at System.ServiceModel.Dispatcher.DispatchOperationRuntime.InvokeEnd(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage7(MessageRpc& rpc) at System.ServiceModel.Dispatcher.MessageRpc.Process(Boolean isOperationContextSet);

The EWS logs for Site B show an HTTP 500 status with a generic error that resembles the following:

ReportException_Message=The remote host closed the connection. The error code is 0x80070057.;ReportException_StackTrace= at System.ServiceModel.Channels.HttpOutput.HostedRequestHttpOutput.HostedResponseOutputStream.CheckWrapThrow(Exception e) at System.ServiceModel.Channels.HttpOutput.HostedRequestHttpOutput.HostedResponseOutputStream.Write(Byte[] buffer; Int32 offset; Int32 count) at System.IO.BufferedStream.FlushWrite() at System.IO.BufferedStream.Flush() at System.Xml.XmlStreamNodeWriter.Flush() at Microsoft.Exchange.Services.Wcf.SoapWcfResponseRenderer.Render(Message message; Stream stream) at Microsoft.Exchange.Services.Wcf.MessageEncoderWithXmlDeclaration.WriteMessage(Message message; Stream stream) at System.ServiceModel.Channels.HttpOutput.WriteStreamedMessage(TimeSpan timeout) at System.ServiceModel.Channels.HttpOutput.Send(TimeSpan timeout) at System.ServiceModel.Channels.HttpRequestContext.OnReply(Message message; TimeSpan timeout) at System.ServiceModel.Channels.RequestContextBase.Reply(Message message; TimeSpan timeout) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.Reply(MessageRpc& rpc);

The connection between the Exchange servers on the two sites for this request is dropped because of a ProxyTimeout setting.

To resolve this issue, increase the ProxyTimeout value on the CAS server by editing the web.config file for EWS. To do this, follow these steps:

  1. Locate the web.config file, and then open the file in Notepad or another text-editing program. The default location is %ExchangeInstallPath%\ClientAccess\exchweb\ews.
  2. In the file, scroll down to find the following statement: <AppSettings>
  3. Add the following line in the <AppSettings> section to increase the time-out value:
    <add key="ProxyTimeout" value="120000" />
  4. Restart the MSExchangeServicesAppPool application pool.

Note The default value for ProxyTimeout is 59000. This value should be increased gradually until the issue is resolved. For example, start by increasing the time-out to 120000. If the issue persists, increase the value to 210000.
More information
For more information, see Start or stop an application pool.
EWS,Outlook For MAC,Large attachment,ProxyTimeout,Cross-Site Proxy

Article ID: 3107326 - Last Review: 12/11/2015 01:49:00 - Revision: 3.0

Microsoft Exchange Server 2010 Enterprise, Microsoft Exchange Server 2010 Standard, Microsoft Outlook 2016 for Mac, Microsoft Outlook for Mac 2011

  • kbsurveynew KB3107326