function emailCheck (emailStr) {
/* check if the entered email addressfits the user@domain format.  It also is used to separate the username from the domain. */
var emailPattern=/^(.+)@(.+)$/
/* 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 email 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
   email address. NOTE: The square brackets are required. */
var ipDomainPattern=/^\[(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})\]$/
/* The following string represents an atom (basically a series of non-special characters.) */
var atom=validChars + '+'
/* The following string represents one word in the typical username. For example, in john.doe@somewhere.com, john and doe are words.
   Basically, a word is either an atom or quoted string. */
var word="(" + atom + "|" + quotedUser + ")"
// The following pattern describes the structure of the user
var userPattern=new RegExp("^" + word + "(\\." + word + ")*$")
/* The following pattern describes the structure of a normal symbolic domain, as opposed to ipDomainPattern, shown above. */
var domainPattern=new RegExp("^" + atom + "(\\." + atom +")*$")
/* Begin with the coarse pattern to simply break up user@domain into different pieces that are easy to analyze. */
var matchArray=emailStr.match(emailPattern)
if (matchArray==null) {
/* Too many/few @'s or something; basically, this address doesn't even fit the general mould of a valid email address. */
	alert("Sorry, this is not a valid email address. Please re-enter your email.")
	return false
}
var user=matchArray[1]
var domain=matchArray[2]
// See if "user" is valid 
if (user.match(userPattern)==null) {
    // user is not valid
    alert("Sorry, this is not a valid email address. Please re-enter your email.")
    return false
}
/* if the email address is at an IP address (as opposed to a symbolic host name) make sure the IP address is valid. */
var IPArray=domain.match(ipDomainPattern)
if (IPArray!=null) {
    // this is an IP address
	  for (var i=1;i<=4;i++) {
	    if (IPArray[i]>255) {
	        alert("Sorry, this is not a valid email address. Please re-enter your email.")
		return false
	    }
    }
    return true
}
// Domain is symbolic name
var domainArray=domain.match(domainPattern)
if (domainArray==null) {
	alert("Sorry, this is not a valid email address. Please re-enter your email.")
    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. */
var atomPattern=new RegExp(atom,"g")
var domArr=domain.match(atomPattern)
var len=domArr.length
if (domArr[domArr.length-1].length<2 || 
    domArr[domArr.length-1].length>3) {
   // the address must end in a two letter or three letter word.
   alert("Sorry, this is not a valid email address. Please re-enter your email.")
   return false
}
// Make sure there's a host name preceding the domain.
if (len<2) {
   var errStr="Sorry, this is not a valid email address. Please re-enter your email."
   alert(errStr)
   return false
}
// If we've gotten this far, everything's valid!
 var errStr="Your email has been submitted to Harvard@Home. You will be notified when new programs are released."
   alert(errStr)
return true;
}