You can’t. Since you use SMTP, in general case, it’s impossible to tell whether delivery succeeded or not. Read SMTP specification. Mail is routed while being delivered, so: There’s no guarantee your message is sent as soon as you call smtp.Send(). Since SMTP is routed, you can’t be sure that some node on the route … Read more
Fixed a few typos in the working code above: MailMessage msg = new MailMessage(); msg.To.Add(new MailAddress(“someone@somedomain.com”, “SomeOne”)); msg.From = new MailAddress(“you@yourdomain.com”, “You”); msg.Subject = “This is a Test Mail”; msg.Body = “This is a test message using Exchange OnLine”; msg.IsBodyHtml = true; SmtpClient client = new SmtpClient(); client.UseDefaultCredentials = false; client.Credentials = new System.Net.NetworkCredential(“your user … Read more