Re: Re: Email Validation built-in? RFC

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 PHP Classes - Free ready to use OOP components written in PHP http://www.phpclasses.org/ PHP Reviews - Reviews of PHP books and other products http://www.phpclasses.org/reviews/ Metastorage - Data object relational mapping layer generator http://www.meta-language.net/metastorage.html