function emailCheck(emailStr,showAlert){

    /* 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 = "\\(\\)><@,;:\\\\\\\"\\.\\[\\]";
    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. */
		if (showAlert) {
			alert("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) {
			if (showAlert) {
				alert("Ths username contains invalid characters.");
			}
            return false;
        }
    }
    for (i = 0; i < domain.length; i++) {
        if (domain.charCodeAt(i) > 127) {
			if (showAlert) {
				alert("Ths domain name contains invalid characters.");
			}
            return false;
        }
    }
    
    // See if "user" is valid 
    
    if (user.match(userPat) == null) {
    
        // user is not valid
        if (showAlert) {
			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) {
				if (showAlert) {
					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) {
			if (showAlert) {
				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) {
		if (showAlert) {
			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) {
		if (showAlert) {
			alert("This address is missing a hostname!");
		}
        return false;
    }
    
    // If we've gotten this far, everything's valid!
    return true;
}