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 Sub SendAsync (
	message As MailMessage,
	userToken As Object
)

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.

Exception Condition
ArgumentNullException

message is null.

-or-

MailMessage.From is null.

InvalidOperationException

This SmtpClient has a SendAsync call in progress.

-or-

There are no recipients specified in MailMessage.To, MailMessage.CC, and MailMessage.Bcc properties.

-or-

DeliveryMethod property is set to Network and Host is null.

-or-

DeliveryMethod property is set to Network and Host is equal to the empty string ("").

-or-

DeliveryMethod property is set to Network and Port is zero, a negative number, or greater than 65,535.

ObjectDisposedException

This object has been disposed.

SmtpException

The connection to the SMTP server failed.

-or-

Authentication failed.

-or-

The operation timed out.

-or-

EnableSsl is set to true but the DeliveryMethod property is set to SpecifiedPickupDirectory or PickupDirectoryFromIis.

-or-

EnableSsl is set to true, but the SMTP mail server did not advertise STARTTLS in the response to the EHLO command.

-or-

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

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.

When sending e-mail using SendAsync to multiple recipients, if the SMTP server accepts some recipients as valid and rejects others, a SmtpException is thrown with a NullReferenceException for the inner exception. If this occurs, SendAsync fails to send e-mail to any of the recipients.

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.

System_CAPS_noteNote

If the EnableSsl property is set to true, and the SMTP mail server does not advertise STARTTLS in the response to the EHLO command, then a call to the Send or SendAsync methods will throw an SmtpException.

The following code example demonstrates calling this method.


Imports System
Imports System.Net
Imports System.Net.Mail
Imports System.Net.Mime
Imports System.Threading
Imports System.ComponentModel
Namespace Examples.SmptExamples.Async
    Public Class SimpleAsynchronousExample
        Private Shared mailSent As Boolean = False
        Private Shared Sub SendCompletedCallback(ByVal sender As Object, ByVal e As AsyncCompletedEventArgs)
            ' Get the unique identifier for this asynchronous operation.
            Dim token As String = CStr(e.UserState)

            If e.Cancelled Then
                Console.WriteLine("[{0}] Send canceled.", token)
            End If
            If e.Error IsNot Nothing Then
                Console.WriteLine("[{0}] {1}", token, e.Error.ToString())
            Else
                Console.WriteLine("Message sent.")
            End If
            mailSent = True
        End Sub
        Public Shared Sub Main(ByVal args() As String)
            ' Command line argument must the the SMTP host.
            Dim client As New SmtpClient(args(0))
            ' Specify the e-mail sender.
            ' Create a mailing address that includes a UTF8 character
            ' in the display name.
            Dim [from] As New MailAddress("jane@contoso.com", "Jane " & ChrW(&HD8) & " Clayton", System.Text.Encoding.UTF8)
            ' Set destinations for the e-mail message.
            Dim [to] As New MailAddress("ben@contoso.com")
            ' Specify the message content.
            Dim message As 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.
            Dim someArrows As New String(New Char() {ChrW(&H2190), ChrW(&H2191), ChrW(&H2192), ChrW(&H2193)})
            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.
            AddHandler client.SendCompleted, AddressOf 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.
            Dim userState As String = "test message1"
            client.SendAsync(message, userState)
            Console.WriteLine("Sending message... press c to cancel mail. Press any other key to exit.")
            Dim answer As String = Console.ReadLine()
            ' If the user canceled the send, and mail hasn't been sent yet,
            ' then cancel the pending operation.
            If answer.StartsWith("c") AndAlso mailSent = False Then
                client.SendAsyncCancel()
            End If
            ' Clean up.
            message.Dispose()
            Console.WriteLine("Goodbye.")
        End Sub
    End Class
End Namespace

SmtpPermission

to connect to the SMTP server. Associated enumeration: Connect

.NET Framework
Available since 2.0
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