This has a very dangerous failure mode: legitimate emails, such as people's replies to Google Groups (and similar), which either themselves end with To unsubsc

This has a very dangerous failure mode: legitimate emails, such as people's replies to Google Groups (and similar), which either themselves end with To unsubscribe from this group and stop receiving emails from it, send an email to GROUP+unsubscribe@googlegroups.com. or which quote other email that ends with the above.