I think whats more likely is that your organisation/email hosting have installed a new spam filter and that is the reason for your reduced spam.
We had a Major problem with spam here about 3 months ago and they started to get really offensive. So we got the go ahead to go and buy a barracuda spam firewall and i can not fault it at all. Took us about half an hour to set up and started blocking spam straight away. Infact it was so easy we thought we had done something wrong.
Since installing it we have gotten 150,000 emails and 80% of them have been blocked as spam with no legit emails getting blocked at all. We still get some spam through but only about 1-2 emails a week.