I tried this and it worked :
Dim Email As New System.Net.Mail.MailMessage("myMail@gmail.com", "otherMail@hccnet.nl")
Email.Subject = "test subject"
Email.Body = "this is a test"
Dim mailClient As New System.Net.Mail.SmtpClient()
Dim basicAuthenticationInfo As New System.Net.NetworkCredential("myUsername", "myPassword")
mailClient.Host = "smtp.gmail.com"
mailClient.Port = 587
mailClient.EnableSsl = True
mailClient.UseDefaultCredentials = False
mailClient.Credentials = basicAuthenticationInfo
mailClient.Send(Email)
Your Line
SMTPServer.Credentials = New System.Net.NetworkCredential("username", "password")
Shouldn't "username" and "password" just be username and password?
Cheers