Sample C# code that works with System.Net.Mail

using System.Net.Mail;
using System.Net;

 public void TestEmail()
        {
            try{
            
                SmtpClient sClient;
                NetworkCredential SMTPUserInfo = new NetworkCredential("Authoritative account", "Authoritative password");
                MailMessage mMessage = new MailMessage();
                mMessage.To.Add(" to email address" );
                mMessage.From = new MailAddress("Authoritative account"); // must use Authoritative account to send from!
             mMessage.Body = "test body";
             mMessage.Subject = "test subject";
             sClient = new SmtpClient("Smtp.mail.microsoftonline.com");
             sClient.Port = 587;
             sClient.EnableSsl = true;
             sClient.UseDefaultCredentials = false;
             sClient.Credentials = SMTPUserInfo;
             sClient.Send(mMessage);
            }
            catch (Exception ex) { throw ex; }
        }

smtp server addresses

o    North America Data Center:  Smtp.mail.microsoftonline.com
o    Europe Data Center:  Smtp.mail.emea.microsoftonline.com
o    Asia Pacific Data Center:  Smtp.mail.apac.microsoftonline.com