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In the past 10 days..one
of our MX server has the following CR stats: 1) 45302:
challenges sent out (new senders) 2) 1558:
challenges respond with 550 SMTP reject code..results in auto-blacklist 3) 696: confirmed
responses to challenges About 3% (1558) of the challenges are easily identified as bogus
senders. The other 97% are either
sent from a mail server that accepts all email for the domain (using auto-gen username) or from a spammer that really doesn’t
care about getting identified. Yahoo, Aol and others firewall at the user level and will
not accept email destined for a non-local user. In fact, spammers are simply bold enough
to use a valid domain using valid return addresses…this somewhat obviates
the impact of RMX Only 1.2% of challenges are responded to. This doesn’t necessarily mean that
users don’t know what to do when challenged…there is no telling how
many of the 45,000 challenges were sent to non-spammers. What is clear is that additional methods
are required. |