This item was deprecated in version 2018r4. Please use POP3SecureSocket as a replacement.


Used to retrieve and manage messages on a POP3 mail server.








List As String



Count As Integer


Index As Integer


Index As Integer, Message As EmailMessage



UserAborted As Boolean


BytesSent As Integer, BytesLeft As Integer



Command As String, Data As String


ErrorCode As Integer, ErrorMessage As String, MessageID As Integer


Index As Integer, Data As EmailMessage

Property descriptions


Address As String

The TCP/IP address to try to connect to.

In this example, the address has been entered into a TextField.

TCPSocket1.Address = TextField1.Text


BytesAvailable As Integer

The number of bytes of data are available in the internal receive buffer.

This property is read-only.

TextField1.Text = Me.BytesAvailable.ToString


BytesLeftToSend As Integer

The number of bytes left in the queue remaining to be sent.

This property is read-only.

This enables you to create a synchronous socket without needing to subclass it.

TextField1.Text = Me.BytesLeftToSend.ToString


EncryptPassword As Boolean

If True, the password is encrypted when being sent to the mail server.

EncryptPassword uses the APOP protocol to transfer the login and password, as described in RFC 1939. If set to false, the POP3 commands USER and PASS are used instead, i.e. the password is sent in clear.

If Me.Caption = "Connect" Then
  Socket1.Address = NthField(ServerFld.Text, ":", 1)
  Socket1.Port = Val(NthField(ServerFld.Text, ":", 2))
  If socket1.Port = 0 Then
    Socket1.Port = 110
  End If
  Socket1.EncryptPassword = True
  Socket1.Username = UsernameFld.Text
  Socket1.Password = PasswordFld.Text

  ProgressBar1.Maximum = 0
  Me.Caption = "Disconnect"
  Me.Caption = "Connect"
End If


Handle As Integer

This is the socket's internal descriptor and it can be used with Declare statements.

This property is read-only.

  • On Windows, Handle is a Socket, suitable for use in Declares on Windows.

  • On macOS and Linux, Handle is a UNIX socket descriptor.

The descriptor is platform-specific. If Handle is less than zero, the descriptor is not available.


IsConnected As Boolean

Indicates whether the socket is currently connected.

This property is read-only.

For TCPSockets, a connection means you can send and receive data and are connected to a remote machine. For UDPSockets, this means that you are bound to the port and are able to send, receive, join or leave multicast groups, or set socket options.

If EasyUDPSocket1.IsConnected Then
  ' proceed using the connection
  MessageBox("Connection failed!")
End If


LocalAddress As String

The local IP address of the computer.

This property is read-only.

Var localIP As String = Socket1.LocalAddress


NetworkInterface As NetworkInterface

Specifies which network interface the socket should use when binding.

You can get the network interface(s) of the user's computer by calling the GetNetworkInterface method of the System module.

Leaving this property set to Nil will use the currently selected interface. In the case of UDPSockets, if you assign a non-Nil value, the socket may not be able to receive broadcast messages. The behavior is OS-dependent; it appears to work on Windows but not on other supported operating systems. If you wish to send broadcast packets out, then you should not bind to a specific interface because the behavior is undefined.

This example specifies that the TCPSocket will use the first Network Interface on the user's computer.

TCPSocket1.NetworkInterface = System.NetworkInterface(0)


Password As String

The password to use for security when connecting to the mail server.


Port As Integer

The port to bind on or connect to.

On most operating systems, attempting to bind to a port less than 1024 causes a Error event to fire with an error number 107 unless the application is running with administrative permissions. This is due to security features built into the underlying OS.

You need to set the port property explicitly before any call to Listen or Connect as the Port property will be modified to reflect what the actual bound port is during the various stages of operation.

For instance, if you listen on port 8080 and a connection comes in, you can check the Port property to ensure that you're still listening on port 8080 (that the port hasn't been hijacked). Or, if you connect to a socket on port 8080, once the connection occurs, you can check to see what port the OS has bound you to. This will be a random-seeming port number.

This trick can be very useful when you do things like Listen on port 0. In that case, the OS will pick a port for you and listen on it. Then you can check the Port property to see which port the OS picked. This functionality is used for various protocols, such as FTP.

This example sets the Port to 8080.

TCPSocket1.Port = 8080


RemoteAddress As String

The address of the remote machine you are connected to.

This property is read-only.

Use this instead of the Address property to determine the address of the machine you are actually connected to.

This example reports the address of the remote machine that the user is connected to. It is in the Connected event.

TextField1.Text = Me.RemoteAddress


Username As String

The username to use for authentication when connecting to the mail server.

Method descriptions



Sends a "NOOP" command to the mail server.

This is a command that asks the server to reply. This can be useful to check that the mail server is still responding and also tells the mail server that you are still connected if there has been no activity for a long period of time.

If successful, the ServerAvailable event handler is called.

In this example, a POP3Socket has been added to the window and named socket1.




Closes the socket's connection, closes any connections the socket may have, and resets the socket.

The only information that is retained after calling Close is the socket's port, address (in the case of TCPSockets), LastErrorCode properties, and data left in the socket's receive buffer. All other information is discarded.

This example closes the EasyTCPSockets that were open. The sockets were added to the main window.




Connects to the mail server and logs in with the values in the Username and *Password *properties.



Asks the server for the number of messages in the mailbox. It triggers the MessageCount event, from which you can get the total.

This is equivalent to the POP3 STAT command.


DeleteMessage(Index As Integer)

Tells the mail server to delete the specified message.



Disconnects the socket, resets it, and fires a SocketCore Error event with a 102 error to let you know that the socket has been disconnected.

This example disconnects the EasyTCPSockets that were opened.




Disconnects from the mail server. This sends a “QUIT” command to the mail server and waits for it to close the connection.

This message logs off from the server. Socket1 is on the layout and has been declared as a POP3Socket.



EndOfFile As Boolean

Returns True when there's no more data left to read.

This code reads the rows and columns of data from a tab-delimited text file into a ListBox:

Var f As FolderItem
Var textInput As TextInputStream
Var rowFromFile, oneCell As String

f = FolderItem.ShowOpenFileDialog("text/plain") ' defined as a FileType
If f <> Nil Then
  textInput = TextInputStream.Open(f)
  textInput.Encoding = Encodings.UTF8

    rowFromFile = textInput.ReadLine
    Var values() As String = rowFromFile.Split(Chr(9))
    ListBox1.ColumnCount = values.Count
    Var col As Integer
    For Each value As String In values
      ListBox1.CellTextAt(ListBox1.LastAddedRowIndex, col) = value
      col = col + 1
    End For
  Loop Until textInput.EndOfFile

End If

This example reads each pair of bytes from a file and writes them in reverse order to a new file. The user chooses the source file using the Open-file dialog box and saves the new file using the Save as dialog box. The EOF property is used to terminate the Do...Loop.

Var readFile As FolderItem = FolderItem.ShowOpenFileDialog("text")
If readFile <> Nil Then
  Var ReadStream As BinaryStream = BinaryStream.Open(readFile, False)
  ReadStream.LittleEndian = True
  Var writeFile As FolderItem = FolderItem.ShowSaveFileDialog("", "")
  If writeFile <> Nil Then
    Var writeStream As BinaryStream = BinaryStream.Create(writeFile, True)
    writeStream.LittleEndian = True
    Do Until ReadStream.EndOfFile
    writeStream = Nil
  End If
  readStream = Nil
End If



Immediately sends the contents of internal write buffers to disk or to the output stream.

This function can be useful in point-to-point communication over sockets and similar connections: To optimize for transmission performance, some types of output streams try to collect small pieces of written data into one larger piece for sending instead of sending each piece out individually. By calling Flush, the data collection is stopped and the data is sent without further delay, reducing latency.

When using this on a stream that ends up as a file on disk, it is useful, too: Any short parts of previously written data are written to disk right away, ensuring the data is actually on disk if the application terminates abruptly, e.g. due to a crash.

Avoid calling this method too often. For example, do not call it between successive Write calls because you'll slow down performance without getting much benefit.

A typical use case would look like this:

mySocket.Write("you typed: ")



Attempts to listen for incoming connections on the currently specified port.

After calling Listen, the Port property will report the actual port you are bound to.


ListMessages([Index As Integer])

Requests a message listing. It fires the ListReceived event. It calls the ListReceived event handler.

This list consists of the message index and the size of the message. If no index is passed, it gets the entire list from the server. If a specific index is passed, it will return just the index message and size of the message.

This is equivalent to the POP3 LIST command.



Lookahead([Encoding As TextEncoding]) As String

Returns a String, containing the data that is available in the internal queue without removing it.

The optional Encoding parameter enables you to specify the text encoding of the data to be returned. The default is Nil. Use the Encodings module to specify an encoding.

This example adds the contents of the internal queue to a TextArea. The Listener EasyTCPSocket has been added to the window.




Polls the socket manually, which allows a socket to be used synchronously.

The EasyTCPSocket "Listener" has been added to the window.




Removes all data from the socket's internal receive buffer. It does not affect the socket's internal send buffer.



Read(Count As Integer, [Enc As TextEncoding]) As String

Reads Count bytes from the input stream and returns a String.

If provided, the optional parameter Enc specifies the text encoding to be defined for the String to be read.

If Count is higher than the amount of bytes currently available in the stream, all available bytes will be returned. Therefore, make sure to always consider the case that you get less than you requested. To see if you received all requested bytes, check the returned string's String property (avoid using Length as it may give a different number if the encoding is not nil).

If not enough memory is available, you get back an empty string.

This example reads the first 1000 bytes from a BinaryStream.

Var readFile As FolderItem = FolderItem.ShowOpenFileDialog("text/plain")
If readFile <> Nil Then
  Var ReadStream As BinaryStream = BinaryStream.Open(readFile, False)
  ReadStream.LittleEndian = True
  TextArea1.Text = ReadStream.Read(1000, Encodings.UTF8)
End If


ReadAll([Encoding As TextEncoding]) As String

Reads all the data from the internal buffer.

This example reads all the data in the buffer into a TextArea.



RetrieveLines(Index As Integer, LineCount As Integer)

Returns the specified number of lines of a message.

The mail server will return the first LineCount of lines that exist in the message you are requesting via the Index parameter. If LineCount is zero, then the mail server returns only the headers for the message.

This is equivalent to the POP3 TOP command.


RetrieveMessage(Index As Integer)

Reads the entire message specified by Index.



Resets the mail server to the state that it was when you logged in.

RollbackServer can be used to undo deletions that occur by accident. The changes aren't committed until the connection is closed. RollbackServer will roll back changes that have not yet been committed by issuing a RSET command to the POP3 server (see RFC 1939 for more details).

On success, the RollbackSuccessful event is fired. Otherwise, the ServerError event is fired.



SendServerCommand(Command As String)

Sends the command specified by Command to the mail server.

This is useful when you need to send a command that in not supported the POP3Socket.


Write(Data As String)

Writes the passed data to the output stream.

Note that in order to make sure that the data actually ends up on disk or gets sent to the socket it is connected to, the stream must either get closed or the Flush method be called. Otherwise, the data, if small, may end up temporarily in a write buffer before either a certain time has passed or more data is written. This buffering increases performance when writing lots of small pieces of data, but may be causing unwanted delays when another process, e.g. the other end of a socket connection, is waiting for the data. Consider calling the Flush method to reduce latencies that this buffering may cause in such cases.

If Write fails, an IOException will be raised.

This example displays the Save As dialog box and writes the contents of the TextArea1 to a text file.

Var f As FolderItem
Var stream As BinaryStream
f = FolderItem.ShowSaveFileDialog(FileTypes1.Text, "Untitled.txt")
If f<> Nil Then
  stream = BinaryStream.Create(f, True)
End If

Event descriptions



Occurs when a connection has been established.

If you have provided a username and password, the authentication has not taken place yet when this event fires. All commands which require that the user is authenticated will return an error. In such a case, move your code into the LoginSuccessful event.



Occurs when the connection with the server has been lost.


ListReceived(List As String)

Executes when the ListMessages method is called.

The List parameter contains the message listing in the format described in RFC 1939.

A typical list is:

1 1253
2 7801
3 534
4 6724
  • "+OK " indicates success

  • Each following line consists in the message number, a space and the message size

  • The final dot indicates the end of the list

  • NOTE that the end of line is normally CRLF, i.e. EndOfLine.

The following code parses the List and store data as an array of Pairs:

Dim theList() As Pair ' Will hold the result
Dim tmp() As String ' Temporary table

tmp = Split(list, EndOfLine.Windows) ' Store each line in the temporary table

If tmp.Ubound < 2 Then ' There is no more than 2 lines, i.e. there is nothing between the leading "+OK " and the trailing "."
  ' The list is empty
Else ' The list is not empty
  ' Walk through the temporary table, avoiding the first and last lines which contain no information
  For i As Integer = 1 To tmp.Ubound - 1
    Dim s As String
    s = tmp(i)
    ' Append a new Pair made of the message number (before the space character) and the message size (after the space character)
    theList.Append(New Pair(Val(NthField(s, " ", 1 )), Val(NthField(s, " ", 2))))

  ' Now we're ready to process the list
  For i As Integer = 0 To theList.Ubound
    Dim p As Pair
    p = theList(i)

    ' p.Left contains the message number as an integer
    ' p.Right contains the message size as an integer

    ' ... Add your code here
End If



Executes when the login process initiated by calling the Connect method is complete.


MessageCount(Count As Integer)

Executes when the mail server replies to a CountMessages call and contains the number of messages in the mailbox.


MessageDeleted(Index As Integer)

Executes when the mail server replies to a DeleteMessage call and contains the index number of the deleted message.


MessageReceived(Index As Integer, Message As EmailMessage)

Executes when a message has been received from the mail server, in response to a call to RetrieveMessage. The Index parameter contains the index number of the retrieved message and the message contents is in Message.



Executes in response to a call to RollbackServer and indicates that the state of the mailbox has been reset.


SendComplete(UserAborted As Boolean)

Occurs when a send has completed.

Use this to determine when all your data has been sent. UserAborted will be True if the user aborted the send by returning True from the SendProgress event. You can use this information to update different status variables or to inform user about the success or failure of the transfer. If the send was completed, this value is False. UserAborted will always be False for UDP sockets.


SendProgress(BytesSent As Integer, BytesLeft As Integer)

Occurs when your network provider queues your data in chunks and is about to send the next chunk.

The parameters indicate the amount of progress that has been made during the send. Returns a Boolean.

Returning True from this event causes the send to be cancelled. This does not close the socket's connection; it only clears the buffer. After all of the data has been transferred you will get a final SendProgress event followed by a SendComplete event.

bytesSent is the number of bytes that were sent in the chunk, not the total number of bytes sent.



Executes when the mail server has replied to a call to CheckServerConnection and indicates that the mail server has replied to the call.


ServerCommandReply(Command As String, Data As String)

Executes in response to a call to SendServerCommand and contains the mail server's response to the command passed.


ServerError(ErrorCode As Integer, ErrorMessage As String, MessageID As Integer)

Executes when a protocol-related error occurs.

The error codes returned in the ErrorCode parameter are as follows:




Unknown Error Message


Incorrect Password




Delete Message Failed


List Messages Failed


Retrieve Lines Failed


Retrieve Message Failed


TopLinesReceived(Index As Integer, Data As EmailMessage)

Executes in response to a call to RetrieveLines. The Index parameter contains the index number of the partial message being retrieved and Data contains the requested lines of the message.


If you use a constructor in a subclass of POP3Socket, you must call the Super class's constructor in your subclass's constructor. The subclass will not work unless this is done.

Specifications of POP3 (Post Office Protocol version 3) are provided in RFC 1939.

Xojo cloud

To access a POP3 server from web apps running on Xojo Cloud, you will first have to use the FirewallPort class to open the port used to connect to the POP3 server.

Dim fwp As New XojoCloud.FirewallPort(110, _
fwp.Open ' This call is synchronous
If fwp.IsOpen() Then
  ' Do what you need to do
End If

Basic usage

As any socket, the POP3 sockets work asynchronously, i.e. the methods trigger exchange of data from/to the POP3 server and results are provided through the available events. If an error occurred, it is sent through the ServerError event.


  1. Once the object is created, set the address of the POP3 server and the port (110 is the default port for POP3 servers not using SSL)

  2. Set the username and password. You can also set EncryptPassword to True if the server supports APOP authentication.

  3. Call the Connect method.

  4. In the LoginSuccessful event, add the code that you want to execute, e.g.:

  5. Call ListMessages to receive the list of messages on the server in the ListReceived event

  6. Call RetrieveMessage to get a message through the MessageReceived event

Sample code

The following example is from the "Email Example" project. The project uses two windows. The "demoWindow" window is used to receive emails. The "sendDemoWindow" window uses the SMTPSecureSocket to send emails.

DemoWindow contains fields for entering the server address, username, and password, a PushButton, and a ListBox for displaying the list of messages. A POP3Socket control, POP3Socket1, has been added to the window. The user clicks the “Connect” PushButton to connect to the mail server, receive email, and list the messages in a ListBox. Its Action event establishes a connection to a POP3 server. It gets the name of the server, username, and password from the contents of the TextFields, ServerFld, UserNameFld, and PasswordFld.

If Me.Caption = "Connect" Then
  Socket1.address = NthField(ServerFld.Text, ":", 1)
  Socket1.Port = Val(NthField(ServerFld.Text, ":", 2))
  If Socket1.Port = 0 Then
    Socket1.Port = 110
  End If

  Socket1.Username = UsernameFld.Text
  Socket1.Password = PasswordFld.Text

  ProgressBar1.Maximum = 0
  Me.Caption = "Disconnect"
  Me.Caption = "Connect"
End If

The following example in the MessageReceived event of the POP3Socket control, displays the message in the multiline TextArea, BodyFld.

Sub MessageReceived(ID As Integer, Email As EmailMessage)
  Dim s As String

  ' display the message
  s = Email.bodyHTML
  If s = "" Then
    s = Email.BodyPlainText
  End If
  BodyFld.Text = ReplaceAll(s, Chr(13) + Chr(10), Chr(13))
End Sub

The LoginSuccessful event executes the CountMessages method that's used to determine whether all the messages have been received.


The POP3Socket's TopLinesReceived event populates the ListBox with summary information on each email that was received.

Sub TopLinesReceived(ID As Integer, Email As EmailMessage)
  ' headers received.  populate the Listbox
  ListBox1.Cell(ListBox1.LastIndex, 1) = Email.FromAddress
  ListBox1.Cell(ListBox1.LastIndex, 2) = Str(ID)

  If ID < MessageTotal Then ' there are still messages left
    Me.RetrieveLines(id + 1, 0) ' get the next message headers
  End If
End Sub


All project types on all supported operating systems.

See also

TCPSocket parent class; * EmailMessage, POP3SecureSocket, URLConnection, SMTPSecureSocket, SocketCore, TCPSocket classes. * Specifications of POP3 (Post Office Protocol version 3): RFC 1939 and updates.