Send SMTP email using System.Net.Mail via Exchange Online (Office 365)

Question

We are testing the new Office 365 beta, and i have a mail account on the Exchange Online service. Now I'm trying to connect a LOB application that can send smtp emails from my test account.

However the Exchange 365 platform requires TLS encryption on port 587, and there is a 'feature' of System.Net.Mail that does not permit Implicit SSL encryption.

Has anyone managed to get C# sending mails via this platform?

I have the following basic code that should send the mail - any advice would be appreciated.

SmtpClient server = new SmtpClient("ServerAddress"); server.Port = 587; server.EnableSsl = true; server.Credentials = new System.Net.NetworkCredential("[email protected]", "password"); server.Timeout = 5000; server.UseDefaultCredentials = false;  MailMessage mail = new MailMessage(); mail.From = new MailAddress("recipent@anyaddress"); mail.To.Add("[email protected]"); mail.Subject = "test out message sending"; mail.Body = "this is my message body"; mail.IsBodyHtml = true;  server.Send(mail); 

Answer 1

Fixed a few typos in the working code above:

MailMessage msg = new MailMessage(); msg.To.Add(new MailAddress("[email protected]", "SomeOne")); msg.From = new MailAddress("[email protected]", "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 name", "your password"); client.Port = 587; // You can use Port 25 if 587 is blocked (mine is!) client.Host = "smtp.office365.com"; client.DeliveryMethod = SmtpDeliveryMethod.Network; client.EnableSsl = true; try {     client.Send(msg);     lblText.Text = "Message Sent Succesfully"; } catch (Exception ex) {     lblText.Text = ex.ToString(); } 

I have two web applications using the above code and both work fine without any trouble.

Answer 2

In year of 2020, these code seems to return exception as

System.Net.Mail.SmtpStatusCode.MustIssueStartTlsFirst or The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.57 SMTP; Client was not authenticated to send anonymous mail during MAIL FROM

This code is working for me.

            using (SmtpClient client = new SmtpClient()             {                 Host = "smtp.office365.com",                 Port = 587,                 UseDefaultCredentials = false, // This require to be before setting Credentials property                 DeliveryMethod = SmtpDeliveryMethod.Network,                 Credentials = new NetworkCredential("[email protected]", "password"), // you must give a full email address for authentication                  TargetName = "STARTTLS/smtp.office365.com", // Set to avoid MustIssueStartTlsFirst exception                 EnableSsl = true // Set to avoid secure connection exception             })             {                  MailMessage message = new MailMessage()                 {                     From = new MailAddress("[email protected]"), // sender must be a full email address                     Subject = subject,                     IsBodyHtml = true,                     Body = "<h1>Hello World</h1>",                     BodyEncoding = System.Text.Encoding.UTF8,                     SubjectEncoding = System.Text.Encoding.UTF8,                  };                 var toAddresses = recipients.Split(',');                 foreach (var to in toAddresses)                 {                     message.To.Add(to.Trim());                 }                  try                 {                     client.Send(message);                 }                 catch (Exception ex)                 {                     Debug.WriteLine(ex.Message);                 }             }