SPAM drop?

[vtlists () wyae de]

Greetings!

Not that I want to complain - but I have observed a massive drop in 
(unsuccessful because blocked) SPAM deliveries - only ~10% compared to only 
2 weeks ago (or only 20% of the average of this year). 
http://www.wyae.de/mailstats.png

Has anyone else observed this? 
What might be the reason? 
Could that effect be amplified even more?

Thanks

Volker Tanger


PS: the massive drop early january was due to a mail server failure, 
   thus does not count...