I read in Bruce's document to not use Geylist Weight Threshold on the SMTP Blocking tab in the Antispam Administration.
It negates the greylisting options he writes.
I thought, maybe I can use that in combination with the spf record.
I have set SPF-weighing up like this:
Pass Weight 0
Fail Weight 6
SoftFail Weight 2
Neutral Weight 2
PermError Weight 5
None Weight 2
So only if SPF check succeeds AND all the other checks are ok, the message won't be greylisted.
If there is something wrong with spf, or a sending domain doesn't have an spf record, it gets 2 points and will be greylisted.
My idea is that a good configured server will pass mail directly and the customer will experience faster reception of mail and still all other received mail will have to pass greylisting.