Dim mmm As CDO.Message = LoadMessageFromFile(MsgFile)
...
    GetMsgInfoCDO.Subject = mmm.Subject
    GetMsgInfoCDO.Body = mmm.TextBody
    For Each att As CDO.IBodyPart In mmm.Attachments
и т.д.

  ' Reference to Microsoft ActiveX Data Objects (в VB6 была ссылка на 2.6, не суть)
  ' Reference to Microsoft CDO for Windows 2000 Library
  Private Function LoadMessageFromFile(ByVal Path As String) As CDO.Message
    Dim Stm As New ADODB.Stream
    Stm.Open()
    Stm.LoadFromFile(Path)
    Dim iMsg As New CDO.Message
    Dim iDsrc As CDO.IDataSource
    iDsrc = iMsg
    iDsrc.OpenObject(Stm, "_Stream")
    LoadMessageFromFile = iMsg
  End Function

    Dim mmm As Object = LoadMessageFromFile(MsgFile)
...
    GetMsgInfoCDO.Subject = mmm.Subject
    GetMsgInfoCDO.Body = mmm.TextBody
    For Each att In mmm.Attachments
и т.д.
  Private Function LoadMessageFromFile(ByVal Path As String) As Object 'CDO.Message
    Dim Stm = CreateObject("ADODB.Stream") 'As New ADODB.Stream
    Stm.Open()
    Stm.LoadFromFile(Path)
    Dim iMsg = CreateObject("CDO.Message") ' As New CDO.Message
    Dim iDsrc As Object ' CDO.IDataSource
    iDsrc = iMsg
    iDsrc.OpenObject(Stm, "_Stream")
    LoadMessageFromFile = iMsg
  End Function

  Private Function LoadMessageFromFile(ByVal Path As String) As Object 'CDO.Message
    Dim Stm = CreateObject("ADODB.Stream") 'As New ADODB.Stream
    Stm.Open()
    Stm.LoadFromFile(Path)
    Dim iMsg = CreateObject("CDO.Message") ' As New CDO.Message
    Dim iDsrc As Object = iMsg.DataSource ' get IDataSource interface
    iDsrc.OpenObject(Stm, "_Stream")
    LoadMessageFromFile = iMsg
  End Function