Could someone please tell me about How MS Exchange fights against spam.
I have experienced Mdaemon server setup. It could use DNS records checks (existance of ptr record, accordination of peer ip address with HELO address dns record, etc.), it could make a delay of data transmitting (spamers MUST send billions of letters, they could not wait for half of a minute to server respond). So point is to minimize letters, which then checked in antispam software.
Which soft (or components) I could use for this?
Maybe I completely wrong in question point, so which is better way to gain less spam without headache.