We can get Internet Headers/Message Headers via WebDAV using PR_TRANSPORT_MESSAGE_HEADERS MAPI property.
PidTagTransportMessageHeaders Canonical Property
http://msdn.microsoft.com/en-us/library/cc815628.aspx
PR_TRANSPORT_MESSAGE_HEADERS http://schemas.microsoft.com/mapi/proptag/0x007D001F
Here is VBScript sample with WebDAV PROPFIND request.
Dim objX, strR, strRes
Set objX = CreateObject("Microsoft.XMLHTTP")
'Change Item URL, Domain, User, Password
objX.Open "PROPFIND", "http://server/exchange/user/Inbox/Item123.EML", FALSE, "Domain\User", "Password"
strR = "<?xml version='1.0'?>"
strR = strR & "<d:propfind xmlns:d='DAV:' xmlns:m='urn:schemas:mailheader:' "
strR = strR & "xmlns:e='http://schemas.microsoft.com/exchange/' xmlns:p='http://schemas.microsoft.com/mapi/proptag/'> "
strR = strR & "<d:prop><d:displayname/><p:0x007D001f/></d:prop></d:propfind>"
objX.SetRequestHeader "Content-type:", "text/xml"
objX.SetRequestHeader "Depth", "1"
objx.SetRequestHeader "translate", "f"
objX.send(strR)
strRes = objX.responseText
Msgbox strRes
And following is sample WebDAV SELECT request.
<?xml version="1.0"?>
<D:searchrequest xmlns:D = "DAV:">
<D:sql>SELECT "urn:schemas:mailheader:to", http://schemas.microsoft.com/mapi/proptag/0x007D001F, "urn:schemas:httpmail:subject" FROM "/exchange/user/Inbox/"
WHERE "DAV:ishidden" = false AND "DAV:isfolder" = false</D:sql>
</D:searchrequest>
Please also refer the article mentioned below related to supportability of working with MAPI properties
The Support Guidelines for Client-Side Messaging Developmenthttp://support.microsoft.com/kb/266353Refer Section: Integrating with Outlook properties