| Re: What this means "(\w|-)+@\w"? [message #175016 is a reply to message #175007] |
Wed, 03 August 2011 13:32   |
Peter H. Coffin
Messages: 245
Registered: September 2010
Karma:
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Senior Member |
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On Tue, 2 Aug 2011 20:53:00 +0000 (UTC), Eli the Bearded wrote:
> In comp.lang.php, Peter H. Coffin <hellsop(at)ninehells(dot)com> wrote:
>> Several years ago, I wrote an email validator that worked fairly will,
>> and handled address cases that hadn't even been thought of yet. It used
>> telnet to fake being a MTA to the MX of record for the domain through
>> enough steps to ask if the receiving MTA would actually accept mail for
>> the address, but stopping short of actually sending anything.
>
> How did it handle temporary errors? Mail is supposed to be retried,
> usually hours later. One common anti-spam technique is to exploit
> that spammers often do not retry and to issue temporary "failure"
> responses to every newly seen (sender,recipent) pair.
Temporary errors were good enough to pass for the "validation of email"
purposes, mostly. There were still some gaps, like "dns responsible for
this domain is not answering (and will never be fixed)" getting treated
as okay, or the MTA being used later having its own out-of-standard
limitations, but the number of false "okay" errors was pretty acceptable
in a few hundred thousand checks, and the false failures was so small
that I never heard anyone talk about any. And in any large collection of
email addresses, you're going to lose about 1% per month dues to domains
being sold, not renewed, accounts closing, people deciding that they've
been getting too much spam and abandoning the account, etc, and the
false okays get lost in that quickly.
--
Premature optimization is the root of all evil.
-- Sir Tony Hoare
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