You'll need to create a .Net wrapper for it by adding a reference: because it depends on ADODB.dll, you'll get Interop.CDO.dll and Interop.ADODB.dll created for you in your bin directory.
There's a lot of information around for sending emails using CDO but almost nothing about using it to read EML files, but I found this page that got me started with iterating through and reading all the eml files in a mailbox directory (like inetpub\mailroot\mailbox\xxx.domain.com\) http://support.microsoft.com/kb/310224
If what you want to do is just open a specific eml file (that you already know the filename of) then there's another way to do it: http://stackoverflow.com/questions/936422/recommendations-on-parsing-eml-files-in-c
Public Shared Function getEmlFileAsMessage(ByVal path As String) As Object Dim msg As CDO.Message = New CDO.MessageClass() Dim stream As ADODB.Stream = New ADODB.StreamClass() Try stream.Open(Type.Missing, ADODB.ConnectModeEnum.adModeUnknown, ADODB.StreamOpenOptionsEnum.adOpenStreamUnspecified, String.Empty, String.Empty) stream.LoadFromFile(path) stream.Flush() msg.DataSource.OpenObject(stream, "_Stream") msg.DataSource.Save() Return msg Catch Return Nothing End Try End Function