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.

    // 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.
        return false;
    }

    var user=matchArray[1]
    var domain=matchArray[2]
    // See if "user" is valid 
    if (user.match(userPat)==null) 
    {
        // user is not 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) 
            {
                // IP-adres invalid
                return false;
            }
   	    }
        // Valid e-mail address
        return true
    }

    // Domain is symbolic name
    var domainArray=domain.match(domainPat)
    if (domainArray==null) 
    {
        // Domainname is invalid
        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), 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.
        return false
    }

    // Make sure there's a host name preceding the domain.
    if (len<2) 
    {
        // Missing a hostname
        return false
    }

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