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Challenge/response emails have largely been dropped. If you implement such a system you end up on blacklists for generating backscatter. If SPF/DKIM ever become
by mike-cardwell 16y ago
Challenge/response emails have largely been dropped. If you implement such a system you end up on blacklists for generating backscatter. If SPF/DKIM ever become ubiquitous then we'll be able to look at using those sorts of systems again.