C#，使用System.Net.Mail.SmtpClient 如何指定使用哪个本地IP地址？

如题，本地有多个IP地址，如何使用不同的IP地址发送邮件，没看到相应的API

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使用 SmtpClient.ServicePoint.BindIPEndPointDelegate

http://msdn.microsoft.com/en-us/library/system.net.servicepoint.bindipendpointdelegate.aspx

var smtpClient = new SmtpClient(...);
smtpClient.ServicePoint.BindIPEndPointDelegate = (servicePoint, remoteEndPoint, retryCount) =>
  new IPEndPoint( IPAddress.Parse( "YOUR LOCAL ADDRESS" ), 0 );