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From: Alfred Hilscher <Alfred.Hilscher@icn.siemens.de>
Subject: Re: Checking validity of an e-mail
Date: 2000/05/18
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Date: 2000-05-18T00:00:00+00:00
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Christophe Gouiran wrote:
> 
> Hi, I want to create a procedure that checks the validity of an e-mail.
> Not only to check the syntax validity but also to check if this mail is a
> real mail (ie when you send an email to it someone receives your message)

1. Check the domain. This is possible by an DNS Query.
2. Check whether the user exist. This should be impossible. There is no
way to look which users are known within a specific mail server. The
only thing you can do is to send a mail, and wait whether you get a
"unknown user" response.

> So, someone knows how to, given an e-mail adress, check it.
> At least, do you know how to go from the email adress to the mail-server ?

This is done by DNS query (query type "MX" = domains mail exchange) with
the domain name.