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  #1 (permalink)  
Old February 16th, 2005, 08:23 AM
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Default How to validate email address


function emailCheck (emailStr) {

/* The following variable tells the rest of the function whether or not
to verify that the address ends in a two-letter country or well-known
TLD. 1 means check it, 0 means don't. */

var checkTLD=1;

/* The following is the list of known TLDs that an e-mail address must end with. */

var knownDomsPat=/^(com|net|org|edu|int|mil|gov|arpa|biz|aero|name|c oop|info|pro|museum)$/;

/* The following pattern is used to check if the entered e-mail address
fits the user@domain format. It also is used to separate the username
from the domain. */

var emailPat=/^(.+)@(.+)$/;

/* The following string represents the pattern for matching all special
characters. We don't want to allow special characters in the address.
These characters include ( ) < > @ , ; : \ " . [ ] */

var specialChars="\\(\\)><@,;:\\\\\\\"\\.\\[\\]";

/* The following string represents the range of characters allowed in a
username or domainname. It really states which chars aren't allowed.*/

var validChars="\[^\\s" + specialChars + "\]";

/* The following pattern applies if the "user" is a quoted string (in
which case, there are no rules about which characters are allowed
and which aren't; anything goes). E.g. "jiminy cricket"@disney.com
is a legal e-mail address. */

var quotedUser="(\"[^\"]*\")";

/* The following pattern applies for domains that are IP addresses,
rather than symbolic names. E.g. joe@[] is a legal
e-mail address. NOTE: The square brackets are required. */

var ipDomainPat=/^\[(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})\]$/;

/* The following string represents an atom (basically a series of non-special characters.) */

var atom=validChars + '+';

/* The following string represents one word in the typical username.
For example, in john.doe@somewhere.com, john and doe are words.
Basically, a word is either an atom or quoted string. */

var word="(" + atom + "|" + quotedUser + ")";

// The following pattern describes the structure of the user

var userPat=new RegExp("^" + word + "(\\." + word + ")*$");

/* The following pattern describes the structure of a normal symbolic
domain, as opposed to ipDomainPat, shown above. */

var domainPat=new RegExp("^" + atom + "(\\." + atom +")*$");

/* Finally, let's start trying to figure out if the supplied address is valid. */

/* Begin with the coarse pattern to simply break up user@domain into
different pieces that are easy to analyze. */

var matchArray=emailStr.match(emailPat);

if (matchArray==null) {

/* Too many/few @'s or something; basically, this address doesn't
even fit the general mould of a valid e-mail address. */

alert("Please enter the email address in correct format (e.g. username@domain.com )");
return false;
var user=matchArray[1];
var domain=matchArray[2];

// Start by checking that only basic ASCII characters are in the strings (0-127).

for (i=0; i<user.length; i++) {
if (user.charCodeAt(i)>127) {
alert("Ths username contains invalid characters.");
return false;
for (i=0; i<domain.length; i++) {
if (domain.charCodeAt(i)>127) {
alert("Ths domain name contains invalid characters.");
return false;

// See if "user" is valid

if (user.match(userPat)==null) {

// user is not valid

alert("The username doesn't seem to be valid.");
return false;

/* if the e-mail address is at an IP address (as opposed to a symbolic
host name) make sure the IP address is valid. */

var IPArray=domain.match(ipDomainPat);
if (IPArray!=null) {

// this is an IP address

for (var i=1;i<=4;i++) {
if (IPArray[i]>255) {
alert("Destination IP address is invalid!");
return false;
return true;

// Domain is symbolic name. Check if it's valid.

var atomPat=new RegExp("^" + atom + "$");
var domArr=domain.split(".");
var len=domArr.length;
for (i=0;i<len;i++) {
if (domArr[i].search(atomPat)==-1) {
alert("The domain name does not seem to be valid.");
return false;

/* domain name seems valid, but now make sure that it ends in a
known top-level domain (like com, edu, gov) or a two-letter word,
representing country (uk, nl), and that there's a hostname preceding
the domain or country. */

if (checkTLD && domArr[domArr.length-1].length!=2 &&
domArr[domArr.length-1].search(knownDomsPat)==-1) {
alert("The address must end in a well-known domain or two letter " + "country.");
return false;

// Make sure there's a host name preceding the domain.

if (len<2) {
alert("This address is missing a hostname!");
return false;

// If we've gotten this far, everything's valid!
return true;

<form name="form" method="post" action="reg_terms.asp" onSubmit="return emailCheck(this.email.value)">
<input type="text" name="email" id="email">

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  #2 (permalink)  
Old February 16th, 2005, 10:01 AM
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Parochial, my hotmail.co.uk appears to be invalid...:)


Joe (Microsoft MVP - XML)
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  #3 (permalink)  
Old February 16th, 2005, 10:56 AM
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I've seen so many variations on this theme - I'm sure I'm not the only one who has - but IMHO the main problem with trying to validate an e-mail is not the format of the address, but the fact that you can't tell whether its a real address until you try to send a mail and it gets bounced (even then it might still be real, but the server might be temporarily down)! So what exactly are these functions trying to prove? I've lost count of the number of times I visit a site which forces me to put in an email address in order to get access to something, but I don't want to give them my real address so I just put anything, fhjkah@gywefyg.com, etc - again, I'm sure I'm not the only one.

...steps off soap box :)

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