1. If it's an email selling ED drugs, it's probably spam.
2. If I get an email and mark "report spam" on it - you probably shouldn't send me the *exact same email* the next day.
3. If the email is full of crazy non-text characters or weird ANSI color codes, it's probably spam.
I mean, Google is letting through emails whose entire body is :
Buy Viagra&Cialis&Tramadol....How can you possibly think that's right?
BTW I think it's very productive to have an atmosphere at your company where anybody can challenge anybody else about the behavior of their functionality. So for example in this case I'd like to see every Google employee forwarding their spam to the spam dev team. But in game dev I'd like to see the artists go up to the tools guy and go "hey dude, our level export takes 30 minutes, WTF." This is one of those things that's very hard to get right. If you have a culture where everyone is friendly and everyone is trying to be the best, it can be welcomed. But if your culture is that everyone is just trying to do the minimum of work and fly under the radar and not talk to each other, then this will be very unwelcome.