I think Port 587 is correct i have tried this before. Be sure to disable your 2 steps gmail account verification.
If it is enabled, Gmail will send you security code either to your mobile or email account then you have to enter that dynamic security code every attempts
BTW here is my code.
Dim mail As New MailMessage
mail.Subject = txtsubject.Text
mail.To.Add("xxx@yahoo.com")
mail.From = New MailAddress("yyyyy@gmail.com")
mail.Body = "Hello World"
Dim smtp As New SmtpClient("smtp.gmail.com")
smtp.EnableSsl = True
smtp.Credentials = New System.Net.NetworkCredential("yyyyy@gmail.com", "xxxxxxxxxxx")
smtp.Port = "587"
smtp.Send(mail)