Retrieves the message part specified by PartID.
def fetch_message_part(part_id: str) -> None: ...
This method retrieves the contents of the message part specified by the PartId property of the message specified by the message_set property. If the local_file property contains a file name, the message part is stored in local_file, and the on_transfer events denote the progress. If the local_file property contains an empty string, the message part is stored in the message_text property, as well as provided through the on_transfer event.
The part identifiers of each message part (if any) are provided through the corresponding on_message_part events.