The remote certificate is invalid according to the validation procedure.

In our ASP.NET Core 1.1 app developed using Visual Studio 2017, we are using MailKiT to send email. But the following code is throwing the above error:

using MailKit.Net.Smtp;
using MimeKit;
using System;

namespace EmailApplication
{
class Program
{
static void Main(string[] args)
{
//Nps: mailer.its.nps.gov port: 25...

The remote certificate is invalid according to the validation procedure.