Libreria a importar: Imports System.Net.Mail

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim msg As System.Net.Mail.MailMessage = New System.Net.Mail.MailMessage()
        Dim Destino As String = "destino@correo.com"
        Dim Origen As String = "correoorigen@gmail.com" 'debe ir cuenta hotmail
        Dim PassWord As String = "clave"
        Dim Cuerpo As String = "Estimado(a):"
        Dim CuerpoMsg As String = "cuerpo del mensaje"
        Dim NombreEnviador As String = "Yo"
        Dim HostMail As String = "smtp.gmail.com" 'para hotmail "smtp.live.com"
        Dim RutaArchivoAdjuntar As String = "C:"
        Dim ArchivoAdjuntar As String = RutaArchivoAdjuntar & "a.a"

        msg.To.Add(Destino)
        msg.From = New Net.Mail.MailAddress(Origen, NombreEnviador, System.Text.Encoding.UTF8)
        msg.Subject = CuerpoMsg
        msg.SubjectEncoding = System.Text.Encoding.UTF8
        msg.Body = Cuerpo
        msg.BodyEncoding = System.Text.Encoding.UTF8
        msg.IsBodyHtml = False
        msg.Attachments.Add(New System.Net.Mail.Attachment(fileName:=ArchivoAdjuntar))

        Dim client As SmtpClient = New SmtpClient()
        client.Credentials = New System.Net.NetworkCredential(Origen, PassWord)
        client.Port = 25 '587
        client.Host = HostMail
        client.EnableSsl = True 'Esto es para que vaya a través de SSL que es obligatorio con GMail
        Try
            client.Send(msg)
        Catch ex As Exception
            MsgBox("ERROR: " & ex.Message)
        End Try
    End Sub