I finally decided to empty my spam box today and discovered it had some 13000 messages taking up 140Mb of space.  Spam now makes up 56% of my email which is pretty insane.  The updated version of spamassassin seems to have helped a little but there’s probably still a few getting through and I really don’t think I should lower the threshold any further – it’s currently at 3 whereas the default is 10.