Leo Bicknell wrote:
* Make sure your mail servers are squeeky clean. Forward and reverse match, valid MX's, they report their own name in SMTP headers, no "untrusted sender used -f", etc. Valid abuse@ for the machine name, and the parent domain are essential. Valid contacts for the domain and IP block are helpful.
In addition to having all the above properly setup so that your mail servers appear squeekly clean from the outside, make sure they ARE squeeky clean - on the inside. You may wish to raise this issue on the spam-l mailing list: <http://www.claws-and-paws.com/spam-l/> The participants on spam-l will be happy to share with you the many ways spammers relay thru web and mail servers, and how to ensure (and test) that your servers can't be abused. All the pre-emptive whitelisting in the world won't help you if your machines are open relays and spammers start sending spew thru your mail servers. There are too many systems that will automatically blacklist your IPs if they start spewing actual spam, and then you will have to go one-by-one to each of them to get unblocked. It's much better to avoid the problem by not letting your machines send any spam in the first place! jc