An HTTP Mail Client in VB.NET

The great thing about the POP mail protocol is that it is a well-documented open standard, making writing a mail client to collect mail from a POP box a relatively painless process. Armed with basic knowledge of POP, or SMTP it is possible to write proxies, which do a variety of useful things, such filter out spam or junk mail, or provide an e-mail answering machine service. Unfortunately, in trying to write a standalone client for Hotmail, the world’s most popular web-based mailing system, the fact that no POP gateway exists rapidly becomes a problem.

Despite the lack of POP-support, connecting to Hotmail without using a web-browser is possible. Outlook Express allows users to retrieve, delete, move and send messages, connecting directly to a standard Hotmail or MSN mailbox. By using a HTTP packet sniffer, it is possible to monitor communication between Outlook Express and Hotmail, making it possible to determine how the direct mailbox connection is made.

Outlook Express uses an undocumented protocol commonly referred to as HTTPMail, allowing a client to access Hotmail using a set of HTTP/1.1 extensions. This article explains some of the features of HTTPMail, and how best to connect to Hotmail using a VB.NET client. The sample source code accompanying this article uses COM interop to leverage XMLHTTP as the transport service. The XMLHTTP component provides a complete HTTP implementation, including authentication together with ability to set custom headers before sending HTTP requests server-side.

Connecting to the HTTPMail Hotmail Gateway

The default HTTPMail gateway for Hotmail boxes is located at http://services.msn.com/svcs/hotmail/httpmail.asp. Although undocumented, the HTTPMail protocol is actually a standard WebDAV service. As we are using VB.NET, we could use the TCP and HTTP classes provided by the .NET framework within the System.Net namespace. Since we are working with WebDAV, it is simpler to use XMLHTTP to connect to Hotmail under C#. Referencing the MSXML2 component provides an interop assembly, which may be accessed directly. Note that in the code snippets contained within this article, variables suffixed with an underscore refer to member fields declared elsewhere within the sample code:

' Get the namespace.
Imports MSXML2
...
' Create the object.
xmlHttp_ = new XMLHTTP()

In order to connect to a secure server, the WebDAV protocol requires HTTP/1.1 authentication. The initial request sent by an HTTPMail client uses the WebDAV PROPFIND method to query for a set of properties. These include the URL of the Hotmail advertisement bar together with the location of mailbox folders:

<?xml version="1.0"?>
<D:propfind xmlns:D="DAV:" xmlns:h="http://schemas.microsoft.com/hotmail/"
<D:prop>
<h:adbar/>
<hm:contacts/>
<hm:inbox/>
<hm:outbox/>
<hm:sendmsg/>
<hm:sentitems/>
<hm:deleteditems/>
<hm:drafts/>
<hm:msgfolderroot/>
<h:maxpoll/>
<h:sig/>
</D:prop>
</D:propfind>

Sending the initial request via XMLHTTP begins by specifying the WebDAV server URL, and generating the initial XML request:

' Specify the server URL.
Dim serverUrl As String = http://services.msn.com/svcs/hotmail/httpmail.asp
' Build the query.
Dim folderQuery As String = Nothing
folderQuery += "<?xml version='1.0'?><D:propfind xmlns:D='DAV:' "
folderQuery += "xmlns:h='http://schemas.microsoft.com/hotmail/' "
folderQuery += "xmlns:hm='urn:schemas:httpmail:'><D:prop><h:adbar/>"
folderQuery += "<hm:contacts/><hm:inbox/><hm:outbox/><hm:sendmsg/>"
folderQuery += "<hm:sentitems/><hm:deleteditems/><hm:drafts/>"
folderQuery += "<hm:msgfolderroot/><h:maxpoll/><h:sig/></D:prop></D:propfind>"

The HTTPXML component provides an open() method used to establish a connection to a HTTP server:

Sub open(method As String, url As String, async As Boolean, user As String, password As String)

The first argument specifies the HTTP method used to open the connection, such as GET, POST, PUT, or PROPFIND. To connect to the Hotmail gateway, we specify the PROPFIND method to query the mailbox. This and other HTTP methods are used to retrieve folder information, collect mail items and send new mail. Note that the open() method allows for the possibility of asynchronous calls (enabled by default) which is preferred for a graphical mail client. Since the sample code is a console application, we set this parameter to false. For authentication, we specify a username and password. Note that under XMLHTTP, the component will display a login window if these parameters are missing and the site requires authentication. To connect to the Hotmail gateway we open the connection, set the PROPFIND request header to our XML-based query, and then send the request with a null body:

' Open a connection to the Hotmail server.
xmlHttp_.open("PROPFIND", serverUrl, False, username, password)
' Send the request.
xmlHttp_.setRequestHeader("PROPFIND", folderQuery)
xmlHttp_.send(Nothing)

Parsing the Mailbox Folder List

The request sent to services.msn.com is typically redirected several times. After load balancing, we are finally connected to a free Hotmail server, and authenticated. This redirection, with appropriate authentication, is handled by the XMLHTTP component. Once connected, the server will also ask us to set various cookies, valid for the current session (again this is all handled automatically by XMLHTTP). Upon sending the initial connection request, the server will return an XML-based response:

' Get the response.
Dim folderList As String = xmlHttp_.responseText

The returned response will contain, among other useful information, the URL locations of the folders within the mailbox. For example:

<?xml version="1.0" encoding="Windows-1252"?>
<D:response>
...
<D:propstat>
<D:prop>
<h:adbar>AdPane=Off*...</h:adbar>
<hm:contacts>http://law15.oe.hotmail.com/...</hm:contacts>
<hm:inbox>http://law15.oe.hotmail.com/...</hm:inbox>
<hm:sendmsg>http://law15.oe.hotmail.com/...</hm:sendmsg>
<hm:sentitems>http://law15.oe.hotmail.com/...</hm:sentitems>
<hm:deleteditems>http://law15.oe.hotmail.com/...</hm:deleteditems>
<hm:msgfolderroot>http://law15.oe.hotmail.com/...</hm:msgfolderroot>
...
</D:prop>
</D:response>
</D:multistatus>

In the sample console application, the two mailbox folders that we are interested in are the inbox and sendmsg folders, used to retrieve and send mail items respectively. There are various ways to parse XML under C#, but since we are confident of our XML structure, System.XML.XmlTextReader provides fast, forward-only access. We initialise the XML reader by converting the XML string data into a string stream:

' Initiate.
inboxUrl_ = Nothing
sendUrl_ = Nothing
' Load the Xml.
Dim reader As New StringReader(folderList)
Dim xml As New XmlTextReader(reader)

The XML is parsed by iterating through each node, picking out the hm:inbox and hm:sendmsg nodes:

' Read the Xml.
While xml.Read()
' Got an element?
If xml.NodeType = XmlNodeType.Element Then
' Get this node.
Dim name As String = xml.Name
' Got the inbox?
If name = "hm:inbox" Then
' Set folder.
xml.Read()
inboxUrl_ = xml.Value
End If
' Got the send message page?
If name = "hm:sendmsg" Then
' Set folder.
xml.Read()
sendUrl_ = xml.Value
End If
End If
End While

Once the URLs for the inbox and outbox which are valid for this session have been determined, it is possible send and retrieve and e-mail.
Enumerating Folder MailItems

Given the URL of a mailbox folder (such as the Inbox folder) we can direct a WebDAV request to the folder's URL in order to list mail items within the folder. The sample console application defines a managed type MailItem, used to store mail information for a folder item. Folder enumeration begins by initalising an array of MailItems:

' Initiate.
Dim mailItems As New ArrayList

To request mail item data, such as the mail subject, and the to and from addresses, we generate the following XML-based WebDAV query:

<?xml version="1.0"?>
<D:propfind xmlns:D="DAV:" xmlns:hm="urn:schemas:httpmail:" xmlns:m="urn:schemas:mailheader:">
<D:prop>
<D:isfolder/>
<hm:read/>
<m:hasattachment/>
<m:to/>
<m:from/>
<m:subject/>
<m:date/>
<D:getcontentlength/>
</D:prop>
</D:propfind>

The followig VB.NET code generates the XML query string:

' Build the query.
Dim getMailQuery As String = Nothing
getMailQuery += "<?xml version='1.0'?><D:propfind xmlns:D='DAV:' "
getMailQuery += "xmlns:hm='urn:schemas:httpmail:' "
getMailQuery += "xmlns:m='urn:schemas:mailheader:'><D:prop><D:isfolder/>"
getMailQuery += "<hm:read/><m:hasattachment/><m:to/><m:from/><m:subject/>"
getMailQuery += "<m:date/><D:getcontentlength/></D:prop></D:propfind>"

This request is sent via XMLHTTP using the PROPFIND method, similar to the way in which the mailbox folder list was requested above. This time round we set the request body to be the query, and folder information is returned. Since we have already been authenticated for this session, there is no need to resupply the username and password on the XMLHTTP open() call:

' Get the mail info.
xmlHttp_.open("PROPFIND", folderUrl, False, Nothing, Nothing)
xmlHttp_.send(getMailQuery)
Dim folderInfo As String = xmlHttp_.responseText

Following a successful request, the server will respond with an XML stream containing information for each MailItem contained within the folder.

<D:multistatus>
<D:response>
<D:href>http://sea1.oe.hotmail.com/cgi-bin/hmdata/...
</D:href>
<D:propstat>
<D:prop>
<hm:read>1</hm:read>
<m:to/>
<m:from>Mark Anderson</m:from>
<m:subject>RE: New Information</m:subject>
<m:date>2002-08-06T16:38:39</m:date> <D:getcontentlength>1238</D:getcontentlength>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
...
Looking at the XML fragment above, we find that contained within each <D:response> node are a set of fields identifying the MailItem, including the <D:href> tag, which will later allow us to retrieve the item. We can again use System.XML.XmlTextReader to parse this XML text stream. We first initalise the stream reader:

' Holders.
Dim mailItem As MailItem = Nothing
' Load the Xml.
Dim reader As New StringReader(folderInfo)
Dim xml As New XmlTextReader(reader)

Parsing Folder Information

In order the parse the XML in a single pass, we create a new MailItem instance on opening the <D:response> element, and store the instance when we reach the end of the tag. In between, we extract and set MailItem fields:

' Read the Xml.
While xml.Read()
' Sections.
Dim name As String = xml.Name
Dim nodeType As XmlNodeType = xml.NodeType
' E-mail?
If name = "D:response" Then
' Start?
If nodeType = XmlNodeType.Element Then
' Create a new mail item.
mailItem = New MailItem()
End If
' End?
If nodeType = XmlNodeType.EndElement Then
' Store the last mail.
mailItems.Add(mailItem)
' Reset.
mailItem = Nothing
End If
End If
' Got an element?
If nodeType = XmlNodeType.Element Then
' Mail field.
If name = "D:href" Then
' Load.
xml.Read()
mailItem.Url = xml.Value
End If
' Mail field.
If name = "hm:read" Then
' Load.
xml.Read()
mailItem.IsRead = xml.Value = "1"
End If
End If
End While ' Load other MailItem fields, etc...

The above code (part of that found the sample console application) enumerates the MailItems found within the given folder. For each MailItem we extract the following fields:
 

XML Node	Description
D:href	The URL used to retrieve this HttpMail item.
hm:read	Flag set if this e-mail is read.
m:to	Who the mail was sent to.
m:from	Who the mail was sent from.
m:subject	The mail subject.
m:date	Timestamp in the format [date]T[time]
D:getcontentlength	The size of this e-mail (in bytes).

The sample code reads the XML nodes as set out above, to extract information for each mail item found within the returned Folder Info XML data stream.

Retrieving Folder Mail

Once MailItems in the folder have been enumerated, the mail URL (valid for the given session) for a MailItem can be used to retrieve the actual e-mail. Sending a HTTP/1.1 GET request to the Hotmail server, at the given URL, does this. The LoadMail() function defined within the sample code takes a MailItem instance, and returns the content of the mailbox e-mail:

' <summary>
' Loads the given mail item.
' </summary>

Public Function LoadMail(ByVal mailItem As MailItem) As String
' Get the Url.
Dim mailUrl As String = mailItem.Url
' Open a connection to the Hotmail server.
xmlHttp_.open("GET", mailUrl, False, Nothing, Nothing)
' Send the request.
xmlHttp_.send(Nothing)
' Get the response.
Dim mailData As String = xmlHttp_.responseText
' Return the mail data.
Return mailData
End Function 'LoadMail

Sending New Mail

In order to retrieve mail, the LoadMail() method (see above) performs a HTTP/1.1 GET request. Similarly, a POST is sent to the sendmsg URL in order to send e-mail from the Hotmail box. The sample console application also contains a SendMail() method which maybe invoked once connected to the mailbox:

' <summary>
' Sends an e-mail.
' </summary>
Public Sub SendMail(ByVal from As String, ByVal fromName As String, ByVal [to] As String, ByVal subject As String, ByVal body As String)
'
End Sub 'SendMail '

We begin by setting up a quote string (used later) as well generating a mail time stamp:

' Quote character.
Dim quote As String = """"
' Generate the time stamp.
Dim now As DateTime = DateTime.Now
Dim timeStamp As String = now.ToString("ddd, dd MMM yyyy hh:mm:ss")

The HTTPMail protocol follows an SMTP-like communication scheme (See RFC 821). Outlook express sends out mail in MIME format, but for demonstrations purposes we simply send a plain text e-mail:

' Build the post body.
Dim postBody As String = Nothing
' Dump mail headers.
postBody += "MAIL FROM:<" + from + ">" + ControlChars.Cr + ControlChars.Lf
postBody += "RCPT TO:<" + [to] + ">" + ControlChars.Cr + ControlChars.Lf
postBody += ControlChars.Cr + ControlChars.Lf
postBody += "From: " + quote + fromName + quote + " <" + from + ">" + ControlChars.Cr + ControlChars.Lf
postBody += "To: <" + [to] + ">" + ControlChars.Cr + ControlChars.Lf
postBody += "Subject: " + subject + ControlChars.Cr + ControlChars.Lf
postBody += "Date: " + timeStamp + " -0000" + ControlChars.Lf
postBody += ControlChars.Cr + ControlChars.Lf
' Dump mail body.
postBody += body

To send the mail, we need to set the Content-Type request header to message/rfc821, indicating that this request contains a body which follows RFC 821. We POST the request body generated above to the sendmsg URL obtained during connection time:

' Open the connection.
xmlHttp_.open("POST", sendUrl_, False, Nothing, Nothing)
' Send the request.
xmlHttp_.setRequestHeader("Content-Type", "message/rfc821")
xmlHttp_.send(postBody)

Given a valid destination mailbox, Hotmail will send the mail to our desired location.

Conclusion

Hotmail is the world's largest provider of free, Web-based e-mail. However, the only non-web mail client with direct access to Hotmail is Outlook Express. Since the HTTPMail protocol is undocumented, other vendors are discouraged from providing a similar service. In this article we saw how to connect to a Hotmail mailbox, enumerate inbox mail items, and send and retrieve e-mail, using VB.NET and the XMLHTTP component. Sample code accompanying this article contains a .NET assembly, demonstrating that connecting to Hotmail via HTTPMail can be as simple as working with any other mail protocol such as POP3, IMAP4 or SMTP.