As I could send a message containing HTML from VB 6.0, I can send the message but I can not with html

Open "ruta donde esta el archivo txt" For Input As #1
    Dim Linea As String, Total As String
    Do Until EOF(1)
    Line Input #1, Linea
    Total = Total + Linea + vbCrLf
    Loop
    Close #1

    Open "ubicación donde esta en .txt pie del mensaje " For Input As #1
    Dim Linea2 As String, pie As String
    Do Until EOF(1)
    Line Input #1, Linea2
    pie = pie + Linea2 + vbCrLf
    Loop
    Close #1

    Set oMail = New clsCDOmail

    With oMail
         'datos para enviar
        .servidor = "xxxxxxxxxxxxx"
        .puerto = xxxx
        .UseAuntentificacion = True
        .ssl = True
        .IsBodyHtml = True
        .Usuario = "xxxxxxxxxxxxxxxxxxxxxxxx"
        .PassWord = "xxxxxxxxxx"

        .Asunto = "Comprobante del mensaje"
        .Adjunto = xxxxx primera ruta 
        .Adjunto2 = xxxxx segunda ruta

        .de = "xxxxxxxxxx"
        .para = "xxxxx"
        .Mensaje = Total & pie


        .Enviar_Backup ' manda el mail

    End With

    Set oMail = Nothing