Over the past while I have noticed a few common things for the Spam, Phishing and Malware emails. Most of these because they are sent from Zombied home computers while often have the IP addresses in the Domain Name for site.
With Exim, I have created a couple of rules that drastically reduces the number of emails that are received. One rule set if for on the connection phase, this will reduce the amount of traffic right at the onset so that the mail server doesn't have to process any of the traffic related to these connections. The second though not RFC Compliant, drops after the HELO stage, again to reduce the amount of processing as possible. Again since my mail server isn't suppose to be recieving email from any DSL or Cable connections, I personally feel this is an advantage.
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