As another coding geek, I suspect that it is easy enough to filter this out as false positives.
I'd suggest we try it with two modifications...
- A key-word radomizer that has say 100 words, but only uses between 5 and 10.
- Individually modify the body of the letter so as to make it custom and not the exact same prose every time.
Other changes could be to randomly inject the "trigger word" throughout the body of the letter.