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|coop|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@[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. */

		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)
		{
			return false;
		}
	}
	for (i=0; i<domain.length; i++)
	{
		if (domain.charCodeAt(i)>127)
		{
			return false;
		}
	}

// See if "user" is valid 

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

// user is not 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)
			{
				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)
		{
			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)
	{
		return false;
	}

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

	if (len<2)
	{
		return false;
	}

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