function isValidEmail (emailStr,inShowAlert) {

/* 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 represents the range of characters allowed as
   the first character in a valid username or domain.  I just made it
   the same as above, but if you want to add a different constraint,
   you would change it here. */

var firstChars=validChars

/* 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 at atom (basically a series of
   non-special characters.) */

var atom="(" + firstChars + 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 course pattern to simply break up user@domain into
   different pieces that are easy to analyze. */

	var booShowAlert = true;
	if(inShowAlert == 0){
		booShowAlert = false;
	}

	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. */
		if(booShowAlert){
			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
		if(booShowAlert){
		    alert("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) {
				if(booShowAlert){
				        alert("Destination IP address is invalid!")
				}
				return false
			}
		}
		return true
	}

	// Domain is symbolic name
	var domainArray=domain.match(domainPat)
	if (domainArray==null) {
		if(booShowAlert){
			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).
	   If there's a country code at the end of the address, the full domain
	   must include a hostname and category (e.g. host.co.uk or host.pub.nl).
	   If it ends in a .com or something, make sure there's a hostname.*/

	/* 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) {
	   // the address must end in a two letter or three letter word.
		if(booShowAlert){
		   alert("The Email address seems incorrect without(.'s)")
		}
		return false
	}//alert(domArr[domArr.length-1].length);

	/* If it ends in a country code, we want to make sure there are at
	   least 2 atoms preceding it (representing host and category (i.e.
	   com, gov, etc.)) */
	if (domArr[domArr.length-1].length== 2 && len<2) {
		var errStr="This address ends in two characters, which is a country"
		errStr+=" code.  Country codes must be preceded by "
		errStr+="a hostname and category (like com, co, pub, pu, etc.)"
		if(booShowAlert){
			alert(errStr)
		}
		return false
	}

	/* If it just ends in .com, .gov, etc., make sure there's a host name.
	   This case can never actually happen because earlier checks take
	   care of this implicitly, but we'll do it anyway. */
	if (domArr[domArr.length-1].length == 3 && len<2) {
		var errStr="This address is missing a hostname!"
		if(booShowAlert){
			alert(errStr)
		}
		return false
	}

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