simplematch.py is too liberal in matching addresses.
See https://bugs.launchpad.net/mailman/+bug/1859011 for more info on this. In short, A bounce was returned containing a string that matched one of simplematch's start patterns but nothing that matched the corresponding end pattern and the address regexp was (?P<addr>[^\s@]+@[^\s@)]+)
. The bounce also contained the full message which included a large attached PDF. simplematch went line by line through the PDF and found thousands of matches, none of which were actually email addresses, and this caused problems in subsequent processing.