[ObsoleteAttribute("This method is obsolete in .NET 4.5+. Use ExecuteCustomCommandAsync instead.")]
public IAsyncResult BeginExecuteCustomCommand(
	string commandString,
	bool multiLineResponse,
	AsyncCallback callback,
	Object state
)

<ObsoleteAttribute("This method is obsolete in .NET 4.5+. Use ExecuteCustomCommandAsync instead.")>
Public Function BeginExecuteCustomCommand ( 
	commandString As String,
	multiLineResponse As Boolean,
	callback As AsyncCallback,
	state As Object
) As IAsyncResult

// To use the code below, import MailBee namespaces at the top of your code.
using MailBee;
using MailBee.Pop3Mail;
using MailBee.Mime;

// Put the code below inside your class.

// XTND XMIT callback function.
private void XtndXmitCallback(IAsyncResult result)
{
    Pop3 pop = (Pop3)result.AsyncState;

    // Process the results of XTND XMIT command.
    try
    {
        pop.EndExecuteCustomCommand();
    }
    catch (MailBeePop3NegativeResponseException)
    {
        MessageBox.Show("XTND XMIT command is not supported. The server responded: " +
            pop.GetServerResponse());
        pop.Disconnect();
        return;
    }

    // Create a mail message to be sent.
    MailMessage msg = new MailMessage();
    msg.From.Email = "jdoe@mydomain.com";
    msg.To.AsString = "kathy@herdomain.com";
    msg.Subject = "Meeting request";
    msg.BodyPlainText = "Hi, Kathy,\r\nCan we meet tomorrow?\r\n\r\nRegards,\r\nJohn";

    // Encode the mail message source as multi-line POP3 request.
    string messageSource = System.Text.Encoding.Default.GetString(msg.GetMessageRawData());
    messageSource = messageSource.Replace("\r\n.", "\r\n..");

    // Send the mail message asynchronously.
    pop.BeginExecuteCustomCommand(messageSource + "\r\n.\r\n",
        false, new AsyncCallback(SubmissionCallback), pop);
}

// Mail message submission callback function.
private void SubmissionCallback(IAsyncResult result)
{
    Pop3 pop = (Pop3)result.AsyncState;

    // Process the results of the mail message submission.
    try
    {
        pop.EndExecuteCustomCommand();
        MessageBox.Show("Message submitted for delivery");
    }
    catch (MailBeePop3NegativeResponseException)
    {
        MessageBox.Show("Message was not submitted. The server responded: " +
            pop.GetServerResponse());
    }

    pop.Disconnect();
}

// The actual code.
private void Form1_Load(object sender, System.EventArgs e)
{
    Pop3 pop = new Pop3();

    pop.Connect("pop.mydomain.com");
    pop.Login("jdoe", "secret");

    // Issue XTND XMIT command asynchronously.
    pop.BeginExecuteCustomCommand("XTND XMIT\r\n", false,
        new AsyncCallback(XtndXmitCallback), pop);
}

' To use the code below, import MailBee namespaces at the top of your code.
Imports MailBee
Imports MailBee.Pop3Mail
Imports MailBee.Mime

' Put the code below inside your class.

' XTND XMIT callback function.
Private Sub XtndXmitCallback(ByVal result As IAsyncResult)
    Dim pop As New Pop3
    pop = result.AsyncState

    ' Process the results of XTND XMIT command.
    Try
        pop.EndExecuteCustomCommand()
    Catch MailBeePop3NegativeResponseException As Exception
        MsgBox("XTND XMIT command is not supported. The server responded: " & _
            pop.GetServerResponse())
        pop.Disconnect()
        Return
    End Try

    ' Create a mail message to be sent.
    Dim msg As New MailMessage
    msg.From.Email = "jdoe@mydomain.com"
    msg.To.AsString = "kathy@herdomain.com"
    msg.Subject = "Meeting request"
    msg.BodyPlainText = "Hi, Kathy,\r\nCan we meet tomorrow?\r\n\r\nRegards,\r\nJohn"

    ' Encode the mail message source as multi-line POP3 request.
    Dim messageSource As String = System.Text.Encoding.Default.GetString(msg.GetMessageRawData())
    messageSource = messageSource.Replace("\r\n.", "\r\n..")

    ' Send the mail message asynchronously.
    pop.BeginExecuteCustomCommand(messageSource + "\r\n.\r\n", False, _
        New AsyncCallback(AddressOf SubmissionCallback), pop)
End Sub

' Mail message submission callback function.
Private Sub SubmissionCallback(ByVal result As IAsyncResult)
    Dim pop As New Pop3
    pop = result.AsyncState

    ' Process the results of the mail message submission.
    Try
        pop.EndExecuteCustomCommand()
        MsgBox("Message submitted for delivery")
    Catch MailBeePop3NegativeResponseException As Exception
        MsgBox("Message was not submitted. The server responded: " & _
            pop.GetServerResponse())
    End Try

    pop.Disconnect()
End Sub

' The actual code.
Private Sub Form11_Load(ByVal sender As Object, ByVal e As System.EventArgs)
    Dim pop As New Pop3
    pop.Connect("pop.mydomain.com")
    pop.Login("jdoe", "secret")

    ' Issue XTND XMIT command asynchronously.
    pop.BeginExecuteCustomCommand("XTND XMIT\r\n", False, _
        New AsyncCallback(AddressOf XtndXmitCallback), pop)
End Sub