Microsoft.Exchange.WebServices.Data -- The underlying connection was closed Error

Question

I am using Microsoft.Exchange.WebServices.Data to connect to Office 365 outlook and pull emails and its attachments. This works correctly on the local development machine. My moved to a server it does not work and fails with the following error message.

Error: 0 : Exception occurred: The request failed. The underlying connection was closed: An unexpected error occurred on a receive.    at Microsoft.Exchange.WebServices.Data.ServiceRequestBase.GetEwsHttpWebResponse(IEwsHttpWebRequest request)
   at Microsoft.Exchange.WebServices.Data.ServiceRequestBase.ValidateAndEmitRequest(IEwsHttpWebRequest& request)
   at Microsoft.Exchange.WebServices.Data.MultiResponseServiceRequest`1.Execute()
   at Microsoft.Exchange.WebServices.Data.ExchangeService.FindItems(FolderId parentFolderId, String queryString, ViewBase view)

The firewall has been opened for the fully qualified domain name for outlook.office365.com from the server. The following is the network captured and having successful ack, it still seem to fail. Please let me know what might be the cause of this issue. Thanks,

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user_1080923 · Answer

Most likely its TLS, Office365 requires that you use TLS 1.2 if the server your running it on is running an older version of the .Net framework this won't be the default https://docs.microsoft.com/en-us/mem/configmgr/core/plan-design/security/enable-tls-1-2-client.

Generally just doing

System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;

will make sure your code always uses TLS 1.2 (as longs a the framework isn't really old)

Microsoft.Exchange.WebServices.Data -- The underlying connection was closed Error

1 Answers