/* From The JavaScript Source!! http://javascript.internet.com */

function emailCheck (emailStr)
{
/* 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. */

/* See if it is blank */
    if (emailStr=='') {
	alert("Email address is required");
	return false;
    }

    /* Now 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 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
	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) {
		alert("Destination IP address is invalid!");
		return false;
	    }
	}
	return true;
    }

    // Domain is symbolic name
    var domainArray=domain.match(domainPat);
    if (domainArray==null) {
	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
   four-letter word (like info), three-letter word (like com, edu, gov)
   or a two-letter word representing country (au, uk, nl) or "co", and
   that there's a hostname preceding the domain or country. */

/* 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 ||
	domArr[domArr.length-1].length>4) {
   // the address must end in a two, three or four letter word.
	alert("The address must end in a three- or four-letter domain, or two letter country.");
	return false;
    }

    // Make sure there's a host name preceding the domain.
    if (len<2) {
	var errStr="This address is missing a hostname!";
	alert(errStr);
	return false;
    }

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