
<!-- Changes:  Sandeep V. Tamhankar (stamhankar@hotmail.com) -->
/* 1.1.2: Fixed a bug where trailing . in e-mail address was passing
(the bug is actually in the weak regexp engine of the browser; I
 simplified the regexps to make it work).
1.1.1: Removed restriction that countries must be preceded by a domain,
so abc@host.uk is now legal.  However, there's still the 
restriction that an address must end in a two or three letter
word.
1.1: Rewrote most of the function to conform more closely to RFC 822.
1.0: Original  */
<!-- This script and many more are available free online at -->
<!-- The JavaScript Source!! http://javascript.internet.com -->

function emailCheck (emailStr) {
/* 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@[123.124.233.4] 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("Email address seems incorrect (check @ and .'s)");
		return false;
	}
	var user=matchArray[1];
	var domain=matchArray[2];

	// See if "user" is valid 
	if (user.match(userPat)==null) {
		// user is not valid
		alert("Email address 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
	var domainArray=domain.match(domainPat);
	if (domainArray==null) {
		alert("The domain name doesn't seem to be valid.");
		return false;
	}

	/* domain name seems valid, but now make sure that it ends in a
	three-letter word (like com, edu, gov) or a two-letter word,
	representing country (uk, nl), and that there's a hostname preceding 
	the domain or country. */

	/* Now we need to break up the domain to get a count of how many atoms
	it consists of. */
	var atomPat=new RegExp(atom,"g");
	var domArr=domain.match(atomPat);
	var len=domArr.length;
	if (domArr[domArr.length-1].length<2 || domArr[domArr.length-1].length>3) {
		// the address must end in a two letter or three letter word.
		alert("The address must end in a three-letter domain, or two letter country.");
		return false;
	}

	// Make sure there's a host name preceding the domain.
	if (len<2) {
		var errStr="This address is missing a hostname!";
		alert(errStr);
		return false;
	}

	// If we've gotten this far, everything's valid!
	return true;
}