Why does filter_var($email, FILTER_VALIDATE_EMAIL) allow test@test?

Question

I was just setting up the validation for a form in which I decided to try using the filter_var function to check the validity of my email address. I can not find out what filter_var actually allows anywhere though (since the documentation is very simple), and I found out that it is allowing an email address like test@test. Doesn't there have to be a .com, .net etc... in the domain?

Thanks for any help!
Metropolis

Answer 1

It is a valid email address. It isn't going to work on the Internet (at least, not today), but it is fine for a local address.

I would assume that the developers are taking the sensible approach to checking email addresses and not building themselves a system that is guaranteed to go out of date as soon as a new TLD is introduced. We have enough email address syntax checkers that reject [email protected] as it is.

Answer 2

No, test can be a local / internal network domain, so that would work. I like it that it correctly validates wrikken@localhost when developing for instance.

A normal nonexistentdomain.foo would have the same problem. If you want to test whether something is delivarable to a host, use getmxrr (and it that fails fall back to gethostbyname()).

Answer 3

The behavior has changed somewhere around April. See bug #49576 and revision 297350.

That e-mail is indeed invalid, or at least that's what the PHP developers understood. The source carries this notice:

/*
 * The regex below is based on a regex by Michael Rushton.
 * However, it is not identical.  I changed it to only consider routeable
 * addresses as valid.  Michael's regex considers a@b a valid address
 * which conflicts with section 2.3.5 of RFC 5321 which states that:
 *
 *   Only resolvable, fully-qualified domain names (FQDNs) are permitted
 *   when domain names are used in SMTP.  In other words, names that can
 *   be resolved to MX RRs or address (i.e., A or AAAA) RRs (as discussed
 *   in Section 5) are permitted, as are CNAME RRs whose targets can be
 *   resolved, in turn, to MX or address RRs.  Local nicknames or
 *   unqualified names MUST NOT be used.

The changelog mentions this bug fix for PHP 5.3.3 and PHP 5.2.14.