function emailCheck (emailStr) {
	
	emailStr = emailStr.toLowerCase();
	/* 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=/^(|arpa|root|aero|asia|biz|cat|com|coop|edu|gov|info|int|jobs|mil|mobi|museum|name|net|org|pro|tel|travel|ac|ad|ae|af|ag|ai|al|am|an|ao|aq|ar|as|at|au|aw|ax|az|ba|bb|bd|be|bf|bg|bh|bi|bj|bm|bn|bo|br|bs|bt|bv|bw|by|bz|ca|cc|cd|cf|cg|ch|ci|ck|cl|cm|cn|co|cr|cu|cv|cx|cy|cz|de|dj|dk|dm|do|dz|ec|ee|eg|er|es|et|eu|fi|fj|fk|fm|fo|fr|ga|gb|gd|ge|gf|gg|gh|gi|gl|gm|gn|gp|gq|gr|gs|gt|gu|gw|gy|hk|hm|hn|hr|ht|hu|id|ie|il|im|in|io|iq|ir|is|it|je|jm|jo|jp|ke|kg|kh|ki|km|kn|kr|kw|ky|kz|la|lb|lc|li|lk|lr|ls|lt|lu|lv|ly|ma|mc|md|mg|mh|mk|ml|mm|mn|mo|mp|mq|mr|ms|mt|mu|mv|mw|mx|my|mz|na|nc|ne|nf|ng|ni|nl|no|np|nr|nu|nz|om|pa|pe|pf|pg|ph|pk|pl|pm|pn|pr|ps|pt|pw|py|qa|re|ro|ru|rw|sa|sb|sc|sd|se|sg|sh|si|sj|sk|sl|sm|sn|so|sr|st|su|sv|sy|sz|tc|td|tf|tg|th|tj|tk|tl|tm|tn|to|tp|tr|tt|tv|tw|tz|ua|ug|uk|um|us|uy|uz|va|vc|ve|vg|vi|vn|vu|wf|ws|ye|yt|yu|za|zm|zw)$/;
	
	/* 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. */
	
	handleMessage("Email address seems incorrect (check @ and .'s)");
	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) {
	handleMessage("Email address contains invalid characters.");
	return false;
	   }
	}
	for (i=0; i<domain.length; i++) {
	if (domain.charCodeAt(i)>127) {
	handleMessage("The domain name contains invalid characters.");
	return false;
	   }
	}
	
	// See if "user" is valid 
	
	if (user.match(userPat)==null) {
	
	// user is not valid
	
	handleMessage("The 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) {
	handleMessage("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) {
	handleMessage("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) {
	handleMessage("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) {
	handleMessage("This address is missing a hostname!");
	return false;
	}
	
	// If we've gotten this far, everything's valid!
	return true;
}