Milter-greylist

Hi,

I am wondering why the greylist_delay time is 30m by default.
Everybody keeps this way or change to something better?

Is there any spammer retrying/queueing the 4xx messages for a later
retry, but giving up before 30 minutes?

Does this happen? So lowering this value I would get more spam and
raising it less spam (as opposed to keep users happy ;-).

Thanks,

Raul Dias