// v 1.1.4
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. */
        
        alert("Email address "+emailStr+" 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) 
        {
            alert("The username in email address "+emailStr+" contains invalid characters.");
            return false;
        }
    }
    for (i=0; i<domain.length; i++) 
    {
        if (domain.charCodeAt(i)>127) 
        {
            alert("The domain name in emaill adress "+emailStr+" contains invalid characters.");
            return false;
        }
    }
    
    // See if "user" is valid 
    
    if (user.match(userPat)==null) 
    {
        // user is not valid
        alert("The username in email address "+emailStr+" 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 in email address "+emailStr+" 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) 
        {
            alert("The domain name in email address "+emailStr+" 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) 
    {
        alert("The address in email address "+emailStr+" must end in a well-known domain or two letter country code.");
        return false;
    }
    
    // Make sure there's a host name preceding the domain.
    if (len<2) 
    {
        alert("The email address "+emailStr+"  is missing a hostname!");
        return false;
    }
    
    // If we've gotten this far, everything's valid!
    return true;
}