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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 async def apply(self, sender: str, recipient: str, mailbox: str, append_msg: AppendMessage) \ -> Tuple[Optional[str], AppendMessage]: """Run the filter and return the mailbox where it should be appended, or None to discard, and the message to be appended, which is usually the same as ``append_msg``. Args: sender: The envelope sender of the message. recipient: The envelope recipient of the message. mailbox: The intended mailbox to append the message. append_msg: The message to be appended. raises: :exc:`~pymap.exceptions.AppendFailure` """

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