the format returned is very fixed:
FLAGS (space) NUMBER (*) DATE (space) SENDER (space) SUBJECT (space) LENGTH
NUMBER will be a left-padded string of up to 4 digits + ")", starting with 5 digits, it is those 5 digits (without the ")")
DATE will be a left-padded string like " 2-Apr-2021" or a non-padded string like "13-Apr-2021"
SENDER is 20 chars long
SUBJECT is 25 chars long
LENGTH is a string like "(1248 chars)" , however it allows more digits and is not padded.