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Posted by Manuel Lemos on 10/24/05 19:56
Hello,
on 10/23/2005 07:21 PM Robin Vickery said the following:
>>> Checking MX records is not reliable at all.
>> I agree that it is less useful today, but it still help catches many
>> domain name typos.
>>
>>> ... would it not make sense for there to be a BUILT-IN PHP function of
>>> a TRUE email syntactic validation?
>> I don't see that being much better than passing a good regular
>> expression to preg_match.
>
> 1. Technically you can't write a regular expression that matches
> *all* valid email addresses as part of the address specification is
> recursive.
>
> ccontent = ctext / quoted-pair / comment
> comment = "(" *([FWS] ccontent) [FWS] ")"
>
> Admittedly 99.99% of people don't even know you *can* comment email
> addresses so it's not a huge problem...
If I am not mistaken, PCRE supports recursive regular expressions.
Anyway, the way I got the RFC that is not quite the form of an address
but the way it may be presented in message header. Meaning, you can add
comments in To: or other e-mail header but in reality the comments are
not part of the address.
> 2. Very few people seem to be capable of recognising a *good* regular
> expression, let alone writing one. It seems clear that validating an
> address is a task that many people want to do, but few can do
> properly. I'd say that's a good reason for making it a built-in
> function.
Yes. What I meant is that just copying a good enough regular expression
would be sufficient to use it. There is no need to understand it.
>> For many years I use this regular expression in popular email validation
>> and forms generation and validation classes.
>>
>>
>> Rather than accepting only valid characters, it rejects all invalid
>> characters as specified in the RFC.
>>
>> ^([-!#$%&'*+./0-9=?A-Z^_`a-z{|}~])+@([-!#$%&'*+/0-9=?A-Z^_`a-z{|}~]+\\.)+[a-zA-Z]{2,6}$
>>
>
> I'm sorry, but this regular expression rejects many perfectly valid
> ASCII characters. It seems to take into account only dot-atoms, not
> quoted-strings. It also rejects valid addresses using domain-literals.
You are right of course. What I wrote is not what I meant. I fixed the
sentence later but I did not realize that the message had already been sent.
What I meant is that despite I use that regular expression for many
years without complaints, it could be improved to reject only invalid
characters, but of course that is not what that expression does.
--
Regards,
Manuel Lemos
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