At Deerfield Hosting we work hard to reduce the spam (unsolicited email) our users receive. About 95% of email arriving at our servers is discarded because we can identify it as spam. None the less, the remaining spam can still be a significant annoyance. The problem with further filtering is false positives. We can’t be throwing away important emails. It’s a hard problem.
We have been noticing for some time the same from address sending to many of our users in different and unrelated domains. Most often this is due to web site scraping, email addresses harvested from web sites. To identify this kind of spam, we have started tracking inbound from and to addresses and generating statistics in real time. When a particular from address exceeds more than a few unrelated domains, subsequent email from that address is blocked.
We welcome feedback on this. If you are noticing that you are getting less spam or if you can see no measurable difference, we want to hear from you.