greylisting?

[Chris Yuzik]

Hi Everyone,

We're catching loads of spam, but would like to take it to the next 
level. From a bit of reading I'm doing, this may be some implementation 
of greylisting. That said, I'm new to the concept of greylisting but it 
seems to make some sense. We're using Sendmail on our server; how easy 
and effective is greylisting? Does it add extra load to the server or 
anything?

Thanks,
Chris