I know that iOS' Mail.app doesn't do automatic spam filtering. However, my ISP's spam filter is quite good, so it automatically marks all suspicious emails with "[SPAM]" on the Subject line. Thus, I'm looking for some way to have iOS' Mail filter automatically move mails with that expression in the Subject to the Junk folder.
It would seem like a basic feature; I mean, mail programs from 20 years ago had this (filter automatically mails according to sender, Subject line or whatever), but I haven't been able to find it. Does it even exist?
EDIT: if possible, I'm looking for an automated way to filter email. We all know already how to manually find and remove unwanted messages, but the whole point of using computers is to save work, after all...