注意：此类在 .NET Framework 2.0 版中是新增的。
允许应用程序使用简单邮件传输协议 (SMTP) 来发送电子邮件。
命名空间:System.Net.Mail
程序集:System（在 system.dll 中）
Dim instance As SmtpClient
public ref class SmtpClient
SmtpClient 类用于将电子邮件发送到 SMTP 服务器以便传递。下表中显示的类用于构造可以使用 SmtpClient 发送的电子邮件。
若要使用 SmtpClient 构造并发送电子邮件，必须指定以下信息：
若要在电子邮件中包括附件，首先使用 Attachment 类创建附件，再使用 MailMessage.Attachments 属性将附件添加到邮件中。根据收件人使用的电子邮件阅读程序和附件的文件类型，某些收件人可能无法阅读附件。对于那些无法以附件的原始格式显示附件的客户端，可以通过使用 MailMessage.AlternateViews 属性来指定替代视图。
可以使用应用程序或计算机配置文件来指定所有 SmtpClient 对象的默认主机、端口和凭据值。有关更多信息，请参见 mailSettings 元素（网络设置）。
若要发送电子邮件并在等待电子邮件传输到 SMTP 服务器期间阻止其他操作，请使用一个同步 Send 方法。若要允许程序的主线程在传输电子邮件的过程中继续执行，请使用一个异步 SendAsync 方法。SendAsync 操作完成时会引发 SendCompleted 事件。若要接收此事件，必须将 SendCompletedEventHandler 委托添加到 SendCompleted 中。SendCompletedEventHandler 委托必须引用处理 SendCompleted 事件通知的回调方法。若要取消异步电子邮件传输，请使用 SendAsyncCancel 方法。
RFC 2821 中定义了 SMTP，这可以在 http://www.ietf.org 上找到。
下面的代码示例演示如何以异步方式发送电子邮件。
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;
public 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.");
}
}
}
#using <System.dll>
using namespace System;
using namespace System::Net;
using namespace System::Net::Mail;
using namespace System::Net::Mime;
using namespace System::Threading;
using namespace System::ComponentModel;
static bool mailSent;
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 != nullptr)
{
Console::WriteLine("[{0}] {1}", token,
e->Error->ToString());
} else
{
Console::WriteLine("Message sent.");
}
mailSent = true;
}
int main(array<String^>^ args)
{
if (args->Length > 1)
{
// Command line argument must the the SMTP host.
SmtpClient^ client = gcnew SmtpClient(args[1]);
// Specify the e-mail sender.
// Create a mailing address that includes a UTF8
// character in the display name.
MailAddress^ from = gcnew MailAddress("jane@contoso.com",
"Jane " + (wchar_t)0xD8 + " Clayton",
System::Text::Encoding::UTF8);
// Set destinations for the e-mail message.
MailAddress^ to = gcnew MailAddress("ben@contoso.com");
// Specify the message content.
MailMessage^ message = gcnew 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 = gcnew String(gcnew array<wchar_t>{L'\u2190',
L'\u2191', L'\u2192', L'\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 += gcnew
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->ToLower()->StartsWith("c") && mailSent == false)
{
client->SendAsyncCancel();
}
// Clean up.
delete message;
client = nullptr;
Console::WriteLine("Goodbye.");
}
else
{
Console::WriteLine("Please give SMTP server name!");
}
}
System.Object
System.Net.Mail.SmtpClient
此类型的任何公共静态（Visual Basic 中的 Shared）成员都是线程安全的，但不保证所有实例成员都是线程安全的。
Windows 98、Windows 2000 SP4、Windows Millennium Edition、Windows Server 2003、Windows XP Media Center Edition、Windows XP Professional x64 Edition、Windows XP SP2、Windows XP Starter Edition
.NET Framework 并不是对每个平台的所有版本都提供支持。有关受支持版本的列表，请参见系统要求。
.NET Framework
受以下版本支持：2.0