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

cexchange-serveroffice365sendmailsystem.net.mail

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("username@mydomain.com", "password");
server.Timeout = 5000;
server.UseDefaultCredentials = false;

MailMessage mail = new MailMessage();
mail.From = new MailAddress("recipent@anyaddress");
mail.To.Add("username@mydomain.com");
mail.Subject = "test out message sending";
mail.Body = "this is my message body";
mail.IsBodyHtml = true;

server.Send(mail);

Best Answer

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 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.

Related Solutions

C# – Send SMTP email testing Microsoft Office 365 in .net

this works for me ( edited from source )

   ThreadPool.QueueUserWorkItem(t =>
            {
                SmtpClient client = new SmtpClient("smtp.office365.com",587);
                client.EnableSsl = true;
                client.Credentials = new System.Net.NetworkCredential("xxx@yyy.com", "password");
                MailAddress from = new MailAddress("xxx@yyy.com", String.Empty, System.Text.Encoding.UTF8);
                MailAddress to = new MailAddress("xxx@yyy.com");
                MailMessage message = new MailMessage(from, to);
                message.Body = "The message I want to send.";
                message.BodyEncoding = System.Text.Encoding.UTF8;
                message.Subject = "The subject of the email";
                message.SubjectEncoding = System.Text.Encoding.UTF8;
                // Set the method that is called back when the send operation ends.
                client.SendCompleted += new SendCompletedEventHandler(SendCompletedCallback);
                // The userState can be any object that allows your callback 
                // method to identify this send operation.
                // For this example, I am passing the message itself
                client.SendAsync(message, message);
            });

        private static void SendCompletedCallback(object sender, AsyncCompletedEventArgs e)
        {
            // Get the message we sent
            MailMessage msg = (MailMessage)e.UserState;

            if (e.Cancelled)
            {
                // prompt user with "send cancelled" message 
            }
            if (e.Error != null)
            {
                // prompt user with error message 
            }
            else
            {
                // prompt user with message sent!
                // as we have the message object we can also display who the message
                // was sent to etc 
            }

            // finally dispose of the message
            if (msg != null)
                msg.Dispose();
        }

C# – SMTP 5.7.57 error when trying to send email via Office 365

In my case after I tried all this suggestion without luck, I contacted Microsoft support, and their suggestion was to simply change the password.

This fixed my issue.

Note that the password wasn't expired, because I logged on office365 with success, however the reset solved the issue.

Lesson learned: don't trust the Office 365 password expiration date, in my case the password would be expired after 1-2 months, but it wasn't working. This leaded me to investigate in my code and only after a lot of time I realized that the problem was in the Office365 password that was "corrupted" or "prematurely expired".

Don't forget every 3 months to "refresh" the password.

Related Topic

The server response was: 5.7.57 SMTP – Office 365