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SmtpClient.SendAsync Method (MailMessage, Object)

Sends the specified e-mail message to an SMTP server for delivery. This method does not block the calling thread and allows the caller to pass an object to the method that is invoked when the operation completes.

Namespace:  System.Net.Mail
Assembly:  System (in System.dll)

[HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading = true)]
public void SendAsync(
	MailMessage message,
	Object userToken
)

Parameters

message
Type: System.Net.Mail.MailMessage

A MailMessage that contains the message to send.

userToken
Type: System.Object

A user-defined object that is passed to the method invoked when the asynchronous operation completes.

ExceptionCondition
ArgumentNullException

MailMessage.From is null.

-or-

MailMessage.To is null.

-or-

message is null.

ArgumentOutOfRangeException

There are no recipients in To, CC, and Bcc.

InvalidOperationException

This SmtpClient has a SendAsync call in progress.

-or-

Host is null.

-or-

Host is equal to the empty string ("").

-or-

Port is zero.

ObjectDisposedException

This object has been disposed.

SmtpException

The connection to the SMTP server failed.

-or-

Authentication failed.

-or-

The operation timed out.

SmtpFailedRecipientsException

The message could not be delivered to one or more of the recipients in To, CC, or Bcc.

NoteNote:

The HostProtectionAttribute attribute applied to this type or member has the following Resources property value: ExternalThreading. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.

To receive notification when the e-mail has been sent or the operation has been canceled, add an event handler to the SendCompleted event. You can cancel a SendAsync operation by calling the SendAsyncCancel method.

After calling SendAsync, you must wait for the e-mail transmission to complete before attempting to send another e-mail message using Send or SendAsync.

Before calling this method, the Host and Port must be set through the configuration files by setting the relevant properties, or by passing this information into the SmtpClient(String, Int32) constructor.

If the SMTP host requires credentials, you must set them before calling this method. To specify credentials, use the UseDefaultCredentials or Credentials properties.

If you receive an SmtpException exception, check the StatusCode property to find the reason the operation failed. The SmtpException can also contain an inner exception that indicates the reason the operation failed.

Your application can detect a server certificate validation error by examining the Error property passed into the SendCompletedEventHandler delegate.

The Timeout property does not have any effect on a SendAsync call.

To send mail and block while it is transmitted to the SMTP server, use one of the Send methods.

The following code example demonstrates calling this method.

using System;
using System.Net;
using System.Net.Mail;
using System.Net.Mime;
using System.Threading;
using System.ComponentModel;
namespace Examples.SmptExamples.Async
{
    public class SimpleAsynchronousExample
    {
        static bool mailSent = false;
        private static void SendCompletedCallback(object sender, AsyncCompletedEventArgs e)
        {
            // Get the unique identifier for this asynchronous operation.
             String token = (string) e.UserState;

            if (e.Cancelled)
            {
                 Console.WriteLine("[{0}] Send canceled.", token);
            }
            if (e.Error != null)
            {
                 Console.WriteLine("[{0}] {1}", token, e.Error.ToString());
            } else
            {
                Console.WriteLine("Message sent.");
            }
            mailSent = true;
        }
        public static void Main(string[] args)
        {
            // Command line argument must the the SMTP host.
            SmtpClient client = new SmtpClient(args[0]);
            // Specify the e-mail sender. 
            // Create a mailing address that includes a UTF8 character 
            // in the display name.
            MailAddress from = new MailAddress("jane@contoso.com", 
               "Jane " + (char)0xD8+ " Clayton", 
            System.Text.Encoding.UTF8);
            // Set destinations for the e-mail message.
            MailAddress to = new MailAddress("ben@contoso.com");
            // Specify the message content.
            MailMessage message = new MailMessage(from, to);
            message.Body = "This is a test e-mail message sent by an application. ";
            // Include some non-ASCII characters in body and subject.
            string someArrows = new string(new char[] {'\u2190', '\u2191', '\u2192', '\u2193'});
            message.Body += Environment.NewLine + someArrows;
            message.BodyEncoding =  System.Text.Encoding.UTF8;
            message.Subject = "test message 1" + someArrows;
            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, the userToken is a string constant.
            string userState = "test message1";
            client.SendAsync(message, userState);
            Console.WriteLine("Sending message... press c to cancel mail. Press any other key to exit.");
            string answer = Console.ReadLine();
            // If the user canceled the send, and mail hasn't been sent yet, 
            // then cancel the pending operation. 
            if (answer.StartsWith("c") && mailSent == false)
            {
                client.SendAsyncCancel();
            }
            // Clean up.
            message.Dispose();
            Console.WriteLine("Goodbye.");
        }
    }
}

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0
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