send mail using SMTP from WCF class library using C#.net throwing error

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IIS7

C#

IIS

C#3.5

SMTP

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Below is the code I am using for sending mail from my local. I have WCF class library project where this code is written. I am calling this function from ASP.net website.

I am getting error :

"Mail not sent : The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required. Learn more at"

Code in c#.net 3.5 :

public String SendMail()
{

System.Net.Mail.MailMessage mail = new System.Net.Mail.MailMessage();
mail.To.Add("to@gmail.com");
mail.From = new MailAddress("from@gmail.com", "Email head", System.Text.Encoding.UTF8);
mail.Subject = "This mail is send from asp.net application";
mail.SubjectEncoding = System.Text.Encoding.UTF8;
mail.Body = "This is Email Body Text";
mail.BodyEncoding = System.Text.Encoding.UTF8;
mail.IsBodyHtml = true;
mail.Priority = MailPriority.High;

SmtpClient client = new SmtpClient();
client.Credentials = new System.Net.NetworkCredential("from@gmail.com", "password");
client.Port = 587;
client.UseDefaultCredentials = false;
client.Host = "smtp.gmail.com";
client.EnableSsl = true;
client.Timeout = 100000;

try
{
client.Send(mail);
return "Mail sent";
}
catch (Exception ex)
{
return "Mail not sent : " + ex.Message.ToString();
}
}

I have done all below settings in my from@gmail.com account.

2-Step Verification Disabled
Access for less secure apps Enabled

Forwarding and POP/IMAP -> Enable POP for all mail (even mail that's already been downloaded)

Forwarding and POP/IMAP -> Enable IMAP