Calling managed code from VB6

.NET code:
 
Imports System
Imports System.Net.Mail
Imports System.Runtime.InteropServices
Namespace sscemail
    <Guid("893F6A58-52B1-11DD-8B0C-046D56D89593"), _
InterfaceType(ComInterfaceType.InterfaceIsIDispatch)> _
    Public Interface _smtp
        <DispId(1)> Function sendmail(ByVal fromAddress As String, ByVal displayName As String, ByVal toAddress As String, ByVal subject As String, ByVal body As String, ByVal html As Boolean, ByVal username As String, ByVal password As String, ByVal host As String, ByVal port As Integer, ByVal enablessl As Boolean) As Boolean
    End Interface
    <Guid("3ce1d9b0-52b7-11dd-ae16-0800200c9a66"), _
         ClassInterface(ClassInterfaceType.None), _
        ProgId("sscemail.smtp")> Public Class smtp
        Implements _smtp
        Public smtp()
        Public Function sendmail(ByVal fromAddress As String, ByVal displayName As String, ByVal toAddress As String, ByVal subject As String, ByVal body As String, ByVal html As Boolean, ByVal username As String, ByVal password As String, ByVal host As String, ByVal port As Integer, ByVal enablessl As Boolean) As Boolean Implements _smtp.sendmail
            Dim msg As System.Net.Mail.MailMessage = New System.Net.Mail.MailMessage()
            msg.To.Add(toAddress)
            msg.From = New MailAddress(fromAddress, displayName, System.Text.Encoding.UTF8)
            msg.Subject = subject
            msg.SubjectEncoding = System.Text.Encoding.UTF8
            msg.Body = body
            msg.BodyEncoding = System.Text.Encoding.UTF8
            msg.IsBodyHtml = html
            msg.Priority = MailPriority.Normal
            'Add the Credentials
            Dim client As SmtpClient = New SmtpClient()
            client.Credentials = New System.Net.NetworkCredential(username, password)
            client.Port = port 'or use 465
            client.Host = host
            client.EnableSsl = enablessl
            Try
                client.Send(msg)
            Catch ex As Exception
                Return False
            End Try
            Return True
        End Function
    End Class
End Namespace
 
 
VB6 code:
Option Explicit
Private Sub cmdSend_Click()
            Dim a As sscemail.smtp
            a = New sscemail.smtp
            MsgBox (a.sendmail("jon@xxx.com", "Jon Califf", "curdie@xxx.com", "Hello this is a test.", "Only testing.", False, "jon@xxx.com", "password", "smtp.gmail.com", 587, True))
            
End Sub