Read email from Exchange Server remotely using .Net

5 August 2009 One Comment

Due to extensive use of email and blackberry, our team get requirement to add new module to enable approval routing via email. Concept is when user click a button on web application, system then will send email to approvers base on pre-define approval routing scheme. Thus approver then will read email and click links within email, which basically a shortcut to send email to specific account with pre-defined subject. A batch process is being set to run every 10 minutes to read any email is being sent by approver on our exchange server and read specific pattern on subject to define if a request would be approved or rejected.

Most challenging part is to read exchange server, since our POP3 access is closed due to security reason, so further reading on this post will describe on how we achieve that through combination of .Net, Exchange Server, XML and DAV access.

Object Reference

Before we start, this project will use some reference on our .Net project, they are

System.Xml
System.Xml.Xsl
MSXML2

MSXML2 is not standard library, it we for some reason couldn’t find it on our system, then we can obtain it for free from MSDN. Just type for “MSXML download” and "MSDN will show you Url for latest update.

Or else we can use .Net HttpWebRequest and HttpWebResponse class instead of using MSXML2, but due to those 2 classes complexity on handling such stream returned, I prefer to have it with MSXML

Exchange Server DAV Url and Operation

To connect to Exchange server, we will use DAV access, basically it will send a HTTP request to DAV Url and get the response. So, we need to know DAV Url for our exchange server, DAV url would normally have pattern as follow: http://exchangeservername/exchange/userlogin/inbox.

Easiest way to get our exchangeserver name if by looking at our outlook account setting, on Outlook –> Tools –> Account Setting –> Change, see Microsoft Exchange Server textbox as below image, that value would be our exchange server name.

Ok, now we know what is our Exchange Server name, now based on that we can figure out some DAV link where we can use to do some operation. Those are:

http://exchangeservername/exchange/userlogin/inbox
PROPFIND, to read all inbox

http://exchangeservername/exchange/userlogin/inbox/emailsubject.eml
DELETE, to delete specific message
X-MS-ENUMATTS, to get list of attachment

http://exchangeservername/exchange/userlogin/inbox/attachment.file
GET, to retrieve email attachment

Connecting to Exchange Server

Below are sample of full function on how we can read exchange email remotely. For other operations like delete or iterate attachment on a message we can modify this code on line 154.

  137 Public Function InboxReadAll() As InboxMessageDataTable
  138         Dim ret As New InboxMessageDataTable
  139 
  140         ‘– Read settings information from web config
  141         Dim ServiceUserId As String = WebConfigurationManager.AppSettings("ServiceLoginId")
  142         Dim ServicePassword As String = WebConfigurationManager.AppSettings("ServicePassword")
  143         Dim ServiceDomain As String = WebConfigurationManager.AppSettings("ServiceDomain")
  144         Dim ServiceInbox As String = String.Format(WebConfigurationManager.AppSettings("ServiceInbox"), ServiceUserId)
  145         Dim LoginIdFull As String = String.Format("{0}\{1}", ServiceDomain, ServiceUserId)
  146 
  147         ‘– variable to handle operation
  148         Dim oXmlHttp As New MSXML2.ServerXMLHTTP40
  149         Dim xmlDOMParamsAttachement As New MSXML2.DOMDocument40
  150         Dim xmlDOMParams As New System.Xml.XmlDataDocument
  151         Dim xmlResponse As XmlNodeList
  152 
  153         ‘– build DAV connection URL
  154         Dim ConnectingUrl As String = String.Format("{0}/inbox", ServiceInbox)
  155 
  156         With oXmlHttp
  157 
  158             ‘– Open DAV Access
  159             .open("PROPFIND", ConnectingUrl, False, LoginIdFull, ServicePassword)
  160             .setRequestHeader("Depth", "1")
  161             .setRequestHeader("Content-type", "xml")
  162             .send()
  163 
  164             ‘– Retrieve request response and load it on XML
  165             Dim Str As String = oXmlHttp.responseText
  166             xmlDOMParams.LoadXml(Str)
  167 
  168             ‘– Get response part of XML
  169             xmlResponse = xmlDOMParams.GetElementsByTagName("a:response")
  170 
  171             ‘– Prepare namespace manager, as response will be coded with some namespace on its element
  172             Dim xmlNs As New XmlNamespaceManager(xmlDOMParams.NameTable)
  173             xmlNs.AddNamespace("a", "DAV:")
  174             xmlNs.AddNamespace("d", "urn:schemas:mailheader:")
  175             xmlNs.AddNamespace("e", "urn:schemas:httpmail:")
  176 
  177             ‘– iterate each node and save it to message datatable
  178             For Each node As XmlNode In xmlResponse
  179                 Dim xmlHref As XmlNode = node.SelectSingleNode("./a:href", xmlNs)
  180                 If Not xmlHref Is Nothing Then
  181                     If xmlHref.InnerText.ToLower.EndsWith(".eml") Then
  182                         Dim newInboxMsg As InboxMessageRow = ret.NewInboxMessageRow
  183                         With newInboxMsg
  184                             .URL = xmlHref.InnerText
  185                             .Subject = node.SelectSingleNode("//d:subject", xmlNs).InnerText
  186                             .FromEmail = node.SelectSingleNode("//e:fromemail", xmlNs).InnerText.ToLower
  187                             .Message = node.SelectSingleNode("//e:textdescription", xmlNs).InnerText
  188                         End With
  189                         ret.Rows.Add(newInboxMsg)
  190                     End If
  191                 End If
  192             Next
  193         End With
  194 
  195         Return ret
  196     End Function