Add Hyperlink to incoming plaintext messages

With this you can get find and open the url without converting the original mail, which might be sufficient for your needs.

Sub LaunchURL(itm As MailItem)

    Dim bodyString As String
    Dim bodyStringSplitLine
    Dim bodyStringSplitWord
    Dim splitLine
    Dim splitWord

    bodyString = itm.Body
    bodyStringSplitLine = Split(bodyString, vbCrLf)

    For Each splitLine In bodyStringSplitLine
        bodyStringSplitWord = Split(splitLine, " ")

        For Each splitWord In bodyStringSplitWord
            If Left(splitWord, 7) = "http://" Then
                Shell ("C:\Program Files\Internet Explorer\IEXPLORE.EXE" & " " & splitWord)
            End If
        Next

    Next

    Set itm = Nothing

End Sub

Private Sub test()
    Dim currItem As MailItem
    Set currItem = ActiveInspector.currentItem
    LaunchURL currItem
End Sub