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
//http://hintdesk.com/asp-net-web-api-identity-and-forgot-password/comment-page-1/
//http://www.binaryintellect.net/articles/df920caf-ba69-4714-938f-fbb358532c0f.aspx
try
{
//From Address
string FromAddress = "[email protected]";
string FromAdressTitle = "Email from ASP.NET Core 1.1";
//To Address
string ToAddress = "[email protected]";
string ToAdressTitle = "Microsoft ASP.NET Core";
string Subject = "Hello World - Sending email using ASP.NET Core 1.1";
string BodyContent = "ASP.NET Core was previously called ASP.NET 5.";

//Smtp Server
string SmtpServer = "smtp.asciitex.com";
//Smtp Port Number
int SmtpPortNumber = 587;

var mimeMessage = new MimeMessage();
mimeMessage.From.Add(new MailboxAddress(FromAdressTitle, FromAddress));
mimeMessage.To.Add(new MailboxAddress(ToAdressTitle, ToAddress));
mimeMessage.Subject = Subject;
mimeMessage.Body = new TextPart("plain")
{
Text = BodyContent

};

using (var client = new SmtpClient())
{

client.Connect(SmtpServer, SmtpPortNumber, false);
// Note: only needed if the SMTP server requires authentication
// Error 5.5.1 Authentication
client.Authenticate(FromAddress, "myFromEmailPassword");
client.Send(mimeMessage);
Console.WriteLine("The mail has been sent successfully !!");
Console.ReadLine();
client.Disconnect(true);

}
}
catch (Exception ex)
{
throw ex;
}
}
}
}