List all messages. A list attempt can only succeed if the client is in the {@link org.apache.commons.net.pop3.POP3#TRANSACTION_STATE TRANSACTION_STATE }. Returns an array of POP3MessageInfo instances, each containing the number of a message and its size in bytes. If there are no messages, this method returns a zero length array. If the list attempt fails, it returns null.
@return An array of POP3MessageInfo instances representing all messagesin the order they appear in the mailbox, each containing the number of a message and its size in bytes. If there are no messages, this method returns a zero length array. If the list attempt fails, it returns null.
@exception IOException If a network I/O error occurs in the process ofsending the list command.