Milter-greylist

I've noticed that the majority of the auto-whitelisted entries in 
greylist.db are so-called 'darkmail', mail for non-existent random 
recipients at our site. An example:

XXX.XXX.XXX.XXX   <>      <858roxana@...>      123456789 AUTO # 
2005-10-19 10:43:21

I do not have lazyaw in use. I am approaching 1 million entries in the 
database and the memory-footprint is becoming an issue. Maybe incomplete 
tuples should be a special case (shorter auto-whitelist?)?

Any thoughts?

Fredrik Nyberg