Re: AOL tried this years ago...
" It's not that filters don't work; rather, it's that they work too well."
No, it's that the people who write the regex cascades needed to implement them are lazy buggers who don't design robustly and fail to test the false-positive cases intelligently.
Had a major problem myself some years ago in the same area when I forwarded myself an e-mail from a major vendor of long and good standing (in order to circumvent a really annoyingly dumbf*ckstupid printer issue I couldn't get fixed and had insufficient permissions to fix myself) and was accused of sending a racist e-mail when I went looking for why it never arrived.
When I tried to suggest the filter was being stupid - for why would a major vendor with so much money they would surely pose an attractive target for the insulted to sue for their last Licorice Allsort be stupid enough to hide a racist term in their invite to come see their latest and greatest? - and suggested a possible reason was the presence of a word such as "companyid" somewhere in the web-clevers I was told that was impossible.
My colleague was a person of color and was responsible for the filters in question, so was feeling sensitive on two counts and not ready for a discussion by any middle-aged racist to excuse his behavior.
So he was appalled when I dumped the web-friendly invite to notepad and found the word "propertyid" loud, proud and entirely innocent of meaning other than an identifier for the hotel shown on the map thingy nestled in the map object descriptor. I imagine it hurt double I had actually called the problem in my original suggestion.
A few days later in a conference call I got yelled at by a vendor who wanted to know why *her* mails weren't getting read and answered. What mails asked a bewildered audience but I asked her to send me her innocent e-mail about a COBOL picture clause to me with the subject inside the mail body and "to Stevie" in the subject.
Sure enough, the Genius Mail Filterer had trapped PIC XXX and flagged it as obscene. COBOL is many things, but obscene isn't one of them (unless you get clever in the Data Division but you can get into Big Trouble for doing that as was explained to me by the chief programmer as she broke my fingers). I called the genius and told him he'd scored another false hit, a biggie, but when he demanded I show him I told him to do his job and examine the logs.
I was tired of his "You're over 50, what do *you* know" attitude by then, and his incompetence was getting the better of my good nature. You'd have thought that my nailing the exact nature of what he'd got wrong the first time around might have clued him in that I'd seen this sort of thing a few times before.
There's no such thing as a filter working "too well". It either works or it doesn't and if it is trapping false positives, it doesn't work and neither did the person who authored the regex.