Amazon SES：请求已中止：请求已取消

Question

通过Amazon SES发送附件超过5 MB的电子邮件时出现以下错误。

The request was aborted: The request was canceled.

at System.Net.ConnectStream.InternalWrite(Boolean async, Byte[] buffer, Int32 offset, Int32 size, AsyncCallback callback, Object state)
   at System.Net.ConnectStream.Write(Byte[] buffer, Int32 offset, Int32 size)
   at Amazon.Runtime.AmazonWebServiceClient.ConfigureWebRequest[X](IRequest`1 wrappedRequest, Byte[] requestData)
   at Amazon.Runtime.AmazonWebServiceClient.Invoke[X,Y](IRequest`1 request, AbstractAWSSigner signer, IResponseUnmarshaller`2 unmarshaller)
   at Amazon.SimpleEmail.AmazonSimpleEmailServiceClient.SendRawEmail(SendRawEmailRequest sendRawEmailRequest)

对此有何建议？