SmtpClient.SendAsync Method (String, String, String, String, Object)

Sends an e-mail message to an SMTP server for delivery. The message sender, recipients, subject, and message body are specified using String objects. 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(
	string from,
	string recipients,
	string subject,
	string body,
	Object userToken
)

Parameters

from
Type: System.String
A String that contains the address information of the message sender.
recipients
Type: System.String
A String that contains the address that the message is sent to.
subject
Type: System.String
A String that contains the subject line for the message.
body
Type: System.String
A String that contains the message body.
userToken
Type: System.Object
A user-defined object that is passed to the method invoked when the asynchronous operation completes.

ExceptionCondition
ArgumentNullException

from is null.

-or-

recipient is null.

ArgumentException

from is Empty.

-or-

recipient is Empty.

InvalidOperationException

This SmtpClient has a SendAsync call in progress.

-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 recipients.

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 properties must be set either through the configuration files or by setting the properties or 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 property.

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.

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.

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.

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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