Validate an E-Mail Address with PHP, the Right Way

Develop a working PHP function to validate e-mail addresses.

The Internet Engineering Task Force (IETF) document, RFC 3696, “Application Techniques for Checking and Transformation of Names” by John Klensin, gives several valid e-mail addresses that are rejected by many PHP validation routines. The addresses: Abc\, customer/ and !def! are all valid. One of the more popular regular expressions found in the literature rejects all of them:


This regular expression allows only the underscore (_) and hyphen (-) characters, numbers and lowercase alphabetic characters. Even assuming a preprocessing step that converts uppercase alphabetic characters to lowercase, the expression rejects addresses with valid characters, such as the slash (/), equal sign (=), exclamation point (!) and percent (%). The expression also requires that the highest-level domain component has only two or three characters, thus rejecting valid domains, such as .museum.

Another favorite regular expression solution is the following:


This regular expression rejects all the valid examples in the preceding paragraph. It does have the grace to allow uppercase alphabetic characters, and it doesn't make the error of assuming a high-level domain name has only two or three characters. It allows invalid domain names, such as

Listing 1 shows an example from PHP Dev Shed ( The code contains (at least) three errors. First, it fails to recognize many valid e-mail address characters, such as percent (%). Second, it splits the e-mail address into user name and domain parts at the at sign (@). E-mail addresses that contain a quoted at sign, such as Abc\ will break this code. Third, it fails to check for host address DNS records. Hosts with a type A DNS entry will accept e-mail and may not necessarily publish a type MX entry. I'm not picking on the author at PHP Dev Shed. More than 100 reviewers gave this a four-out-of-five-star rating.

One of the better solutions comes from Dave Child's blog at ILoveJackDaniel's (, shown in Listing 2 ( Not only does Dave love good-old American whiskey, he also did some homework, read RFC 2822 and recognized the true range of characters valid in an e-mail user name. About 50 people have commented on this solution at the site, including a few corrections that have been incorporated into the original solution. The only major flaw in the code collectively developed at ILoveJackDaniel's is that it fails to allow for quoted characters, such as \@, in the user name. It will reject an address with more than one at sign, so that it does not get tripped up splitting the user name and domain parts using explode("@", $email). A subjective criticism is that the code expends a lot of effort checking the length of each component of the domain portion—effort better spent simply trying a domain lookup. Others might appreciate the due diligence paid to checking the domain before executing a DNS lookup on the network.



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Great article, just a slight fix

David's picture

This is terrific.

There is some sort of typo in the part of the code in Listing 9 where you check the A and MX DNS records, which make this break as written.

if ($isValid && !(checkdnsrr($domain,"MX") ||

if ($isValid && !((checkdnsrr($domain,"MX")) ||

seems to make it work.

your fix works for me too

cruzanmo's picture

Thanks for the awesome script!

I ran into the same error with that line, and your fix made it work for me too!

Your format validation code

Anonymous's picture

Your format validation code will inappropriately permit an all numeric TLD.
“There is an additional rule that essentially requires that top-level domain names not be all- numeric.“ - RFC 3696 - 2

Sure your DNS lookup up would fail, but what is the point of validating the format if you are just going to do a DNS lookup anyway for a domain name that should have already been deemed invalid by the format validation code.

Format validation and existence verification (DNS lookup) serve different purposes, and just because a domain name does not exist does not mean the format is not valid.

There are so many holes in your code, whoever paid you for this write-up is highly deserving of a total refund. If you are going to title such an article as "... the Right Way", you could at least do it the Right Way.

The code at is actually better, and even includes code for verifying actual existence of an eMailbox. is busted

Anonymous's picture

The code at is wrong -- it does not seem to match the RFC at all. Just try the examples given in this article as well as more common cases like:
foo <>

Working Code & Extensive Regular Expressions

Anonymous's picture

Working Code with Extensive use of Regular Expressions for validating email address format.

Check it out and see if you can find any faults.

Email address validation head-to-head

Dominic Sayers's picture

Yes, there are some faults with the Simon Slick code. It's also worth pointing out that both Simon Slick and Doug Lovell's code is copyright All Rights Reserved. You can't use it in your project.

I've written about some public-domain validation functions here:

The Simon Slick code fails on some of the examples in RFC3696.

As some of these comments have pointed out, there are a lot of RFCs that cover this ground. For what it's worth, I believe my function complies with RFCs 1123, 2396, 3696, 4291, 4343, 5321 & 5322.

RFC Compliance

NOYB's picture

RFC Compliance

Backslash is not an RFC compliant component of an non-quoted email address local-part. May have been in the past, but not anymore, and has not be since the publication of RFC 2822 (2001). Move on folks.

This is also reinforced by RFC 3696 (2004).

3. Restrictions on email addresses

Without quotes, local-parts may consist of any combination of
alphabetic characters, digits, or any of the special characters

! # $ % & ' * + - / = ? ^ _ ` . { | } ~

period (".") may also appear, but may not be used to start or end the
local part, nor may two or more consecutive periods appear. Stated
differently, any ASCII graphic (printing) character other than the
at-sign ("@"), backslash, double quote, comma, or square brackets may
appear without quoting. If any of that list of excluded characters
are to appear, they must be quoted.

Also see the RFC3696 Errata

These are not RFC compliant:

And should have read as:
"Fred\ Bloggs"

Also, "the upper limit on address lengths (local-part@domain-part) should normally be considered to be 256."

And as someone already alluded to, the domain name is now, for quite some time I might add, allowed to begin with a digit.

You need to update your code, test data and this article.

RFC Compliance

NOYB's picture

Also the quoted string check appears would allow null (x00). According to RFC 2822 3.2.5. Quoted strings and 3.2.1. Primitive Tokens the permitted NO-WS-CTL characters are x01-x08, x0B, x0E-x1F, x7F. This does not include the null character x00.

RFC 2822
4.1. Miscellaneous obsolete tokens
The obs-char and obs-qp elements each add ASCII value 0.

Appendix B. Differences from earlier standards
Items marked with an asterisk (*) below are items which
appear in section 4 of this document and therefore can no longer be
12. ASCII 0 (null) removed.*


Tom Burt's picture

So should the e-mail address be accepted or not? It fails to satisfy requirement #7 above but I guess the code in Listing 9 would accept it.

It is working good

coderbari's picture

I tested it with many options and its working fine :D