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.
Assembly: System (in System.dll)
[HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading = true)] public void SendAsync( string from, string recipients, string subject, string body, Object userToken )
- Type: System.Object
A user-defined object that is passed to the method invoked when the asynchronous operation completes.
from is null.
recipient is null.
from is Empty.
recipient is Empty.
This object has been disposed.
The connection to the SMTP server failed.
The operation timed out.
EnableSsl is set to true, but the SMTP mail server did not advertise STARTTLS in the response to the EHLO command.
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.
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 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.
To send mail and block while it is transmitted to the SMTP server, use one of the Send methods.
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 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.