How can I make SMTP authenticated in C#

Question

I create new ASP.NET web application that use SMTP to send message. The problem is the smtp was not authenticated from who send the message.

How can I make SMTP authenticated in my program? does C# have a class that have attribute for enter username and password?

Adorable

Answer 1

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

using(SmtpClient smtpClient = new SmtpClient())
{
    var basicCredential = new NetworkCredential("username", "password"); 
    using(MailMessage message = new MailMessage())
    {
        MailAddress fromAddress = new MailAddress("[email protected]"); 

        smtpClient.Host = "mail.mydomain.com";
        smtpClient.UseDefaultCredentials = false;
        smtpClient.Credentials = basicCredential;

        message.From = fromAddress;
        message.Subject = "your subject";
        // Set IsBodyHtml to true means you can send HTML email.
        message.IsBodyHtml = true;
        message.Body = "<h1>your message body</h1>";
        message.To.Add("[email protected]"); 

        try
        {
            smtpClient.Send(message);
        }
        catch(Exception ex)
        {
            //Error, could not send the message
            Response.Write(ex.Message);
        }
    }
}

You may use the above code.

Garbo

where is the username and password coming from ? and what is mail.mydomain.com ? is that he DNS name ? – Gwenn

they're your email address and password, mail.mydomain.com is your SMTP server (e.g. smtp.gmail.com). – Garbo

You should you wrap the MailMessage object in a using statement (or call Dispose on it after your done), right? – Seto

Usually you'll also need to configure a port. This can be done by using the Port Property like smtpClient.Port(123) – Diamine

@Arief: Hi can you check my question? #56605350 any suggestion about how to make our send mail function, not as external senders? – Capillarity

Answer 2

Ensure you set SmtpClient.Credentials after calling SmtpClient.UseDefaultCredentials = false.

The order is important as setting SmtpClient.UseDefaultCredentials = false will reset SmtpClient.Credentials to null.

Ream

When using Sendgrid and the order is wrong - it will return error: "Mailbox unavailable. The server response was: Unauthenticated senders not allowed". Setting Credentials after the UseDefaultCredentials flag fixes this problem – Gujarati

based on the implementation, you don't even need to set UseDefaultCredentials if you are already setting Credentials since they are both based on the same underlying value. – Datnow

Answer 3

Set the Credentials property before sending the message.

Godolphin

Answer 4

To send a message through TLS/SSL, you need to set Ssl of the SmtpClient class to true.

string to = "[email protected]";
string from = "[email protected]";
MailMessage message = new MailMessage(from, to);
message.Subject = "Using the new SMTP client.";
message.Body = @"Using this new feature, you can send an e-mail message from an application very easily.";
SmtpClient client = new SmtpClient(server);
// Credentials are necessary if the server requires the client 
// to authenticate before it will send e-mail on the client's behalf.
client.UseDefaultCredentials = true;
client.EnableSsl = true;
client.Send(message);

Lava

write some code example about SSL vs SMTP Client to make better answer – Barnaby

Answer 5

How do you send the message?

The classes in the System.Net.Mail namespace (which is probably what you should use) has full support for authentication, either specified in Web.config, or using the SmtpClient.Credentials property.

Artair

Answer 6

In my case even after following all of the above. I had to upgrade my project from .net 3.5 to .net 4 to authorize against our internal exchange 2010 mail server.

Rape

Answer 7

Add MailKit through NuGet Package Manager, then use the following code:

using MailKit.Net.Smtp;
using MailKit.Security;
using MimeKit;
using MimeKit.Text;

using (SmtpClient smtpClient = new SmtpClient())
{
    using (MimeMessage message = new MimeMessage())
    {
        try
        {
            var email = new MimeMessage();
            email.From.Add(MailboxAddress.Parse(@"<sender email>"));
            email.To.Add(MailboxAddress.Parse("<recipient email>"));
            email.Subject = "<subject here>";
            email.Body = new TextPart(TextFormat.Html) { Text = "<h1>your message body</h1>" };
            var smtp = new SmtpClient();
            await smtp.ConnectAsync("smtp.<provider>.com", 587, SecureSocketOptions.StartTls);
            await smtp.AuthenticateAsync(@"<sender email>", @"<password>");
            await smtp.SendAsync(email);
            await smtp.DisconnectAsync(true);
        }
        catch (Exception ex)
        {
            //Error, could not send the message
            // Do something
        }
    }
}

The method smtp.AuthenticateAsync(user, password) is where you pass a username/email and a password/key

Replace the values in angle brackets with the suitable values from your side

Lawry