C#

The request failed. The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.

using System.Net;
using System.Net.Mail;
using Microsoft.Exchange.WebServices;
using System.Security.Cryptography;
using System.Security.Cryptography.X509Certificates;

        private void emailNotifyUser ()
        {
Microsoft.Exchange.WebServices.Data.ExchangeService service = new Microsoft.Exchange.WebServices.Data.ExchangeService(Microsoft.Exchange.WebServices.Data.ExchangeVersion.Exchange2010_SP1);
            service.Credentials =
                new Microsoft.Exchange.WebServices.Data.WebCredentials("you@you.com", "password1", "domain.com);
            service.TraceEnabled = true;
            service.TraceFlags = Microsoft.Exchange.WebServices.Data.TraceFlags.All;
            service.Url = new Uri("HTTPS://xxxxxxx/EWS/Exchange.asmx"); // https://xxxxxxx.xxx/autodiscover/autodiscover.xml
            //service.AutodiscoverUrl(To,
            //    RedirectionUrlValidationCallback);
            //ServicePointManager.ServerCertificateValidationCallback = new System.Net.Security.RemoteCertificateValidationCallback
            //(
            //   delegate { return true; }
            //);
            // trust sender
            //System.Net.ServicePointManager.ServerCertificateValidationCallback
            //                = ((sender, cert, chain, errors) => cert.Subject.Contains("nsc-cas-01"));
            ServicePointManager.ServerCertificateValidationCallback += new System.Net.Security.RemoteCertificateValidationCallback(ValidateRemoteCertificate);
            Microsoft.Exchange.WebServices.Data.EmailMessage email = new Microsoft.Exchange.WebServices.Data.EmailMessage(service);
            email.ToRecipients.Add(To);
            email.Subject = "HelloWorld";
            email.Body = new Microsoft.Exchange.WebServices.Data.MessageBody("First email using EWS Managed API");
            email.Body.BodyType = Microsoft.Exchange.WebServices.Data.BodyType.HTML;
            email.Send();
}

private static bool ValidateRemoteCertificate(object sender, X509Certificate cert, X509Chain chain, System.Net.Security.SslPolicyErrors policyErrors)
{
    bool result = false;
    if (cert.Subject.ToUpper().Contains("cas-server-name"))
    {
        result = true;
    }

    return result;
}