Special characters password with smtpclient

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VB

Hi,
I use Vb.net (2005 and 2013).
I use this code sending emails:

Dim SmtpServer As New SmtpClient()
            Dim mail As New MailMessage()
            SmtpServer.Credentials = New _
		Net.NetworkCredential("username@gmail.com", "password")
            SmtpServer.Port = 587
            SmtpServer.Host = "smtp.gmail.com"
            mail = New MailMessage()
            mail.From = New MailAddress("YOURusername@gmail.com")
            mail.To.Add("TOADDRESS")
            mail.Subject = "Test Mail"
            mail.Body = "This is for testing SMTP mail from GMAIL"
            SmtpServer.Send(mail)

and it works fine but only if credential password has got no special characters like '@','!',...

What I have tried:

I have tried with some smtp servers like gmail, register, ecc.
I have tried both with .net 2.0 and .net 4.5.1

Thank a lot!