How to find SMTP Host and port number for sending emails in ASP.Net

Hello 

I want to send email thought asp.net page

for that I need to find SMTP Host and port number 

below is my code 

  Dim EMail As New MailMessage

        EMail.From = New MailAddress(Emailtaxebox.Text)

        EMail.[To].Add(New MailAddress("sa@gmail.com"))

        EMail.Subject = Firstnametextbox.Text + lastnametextbox.Text + "Registerd"

        EMail.Body = " This is content "

        EMail.IsBodyHtml = True

        Dim Client As New SmtpClient()

        Client.Port = 25

        Client.Send(EMail)

can any one tell me how to find SMTP port and host name ? 

I used default one  its gives me error 

No connection could be made because the target machine actively refused it 

Thank you