For the past month or so, my company has been using a spam blocking technique called “greylisting”, and I’m willing to swear by it. It’s the best ever.
It works like this (all automatic and invisible and stuff): The first time I get mail from a particular source, I reject it with a “transient” error. Basically, I say “not right now, try again in a little while.” A well behaved internet mail agent backs off and tries again in 15 minutes or so. Any sender whose message comes back like this is “whitelisted”, and their stuff comes through on the first pass from that point onwards.
Spam senders, on the other hand, frequently turn off this “resend” capability. The reason for this is that the lists of email addresses they use are so filled with incorrect addresses, their mailers would spend all their time re-sending to failed accounts. Because they’re bulk mailers, they pretty much have to live this way.
Summary: I’m only ever going to receive mail that comes from a well behaved mail agent. It’s cut my spam remarkably. It’s also enabled calculation of the following statistic: 97% of the email to me comes from poorly behaved mail agents.
3% of my mail is real. 97% is unsolicited crap.
It’s enough to make me question my unflinching faith in the goodness of humanity.
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