This javascript cut & paste code snippet will help to ensure that an e-mail address provided in a form submission contains a proper prefix '@' sign, and an appropriate suffix (.com, .net, etc.).

Insert this code into your HEAD of HTML

<!-- // == This Script Free To Use Providing This Notice Remains == // // == This Script Has Been Found In The http://www.DesignerWiz.com Javascript Public Archive Library == // // == NOTICE: Though This Material May Have Been In A Public Depository, Certain Author Copyright Restrictions May Apply == // --><script language="JavaScript" type="text/javascript"> <!-- Begin function emailCheck() { txt=document.isn.email.value; if (txt.indexOf("@")<3){ alert("I'm sorry. This email address appears incorrect. Please" +" check the prefix and '@' sign."); return false; } if ((txt.indexOf(".com")<5)&&(txt.indexOf(".org")<5) &&(txt.indexOf(".gov")<5)&&(txt.indexOf(".net")<5) &&(txt.indexOf(".mil")<5)&&(txt.indexOf(".edu")<5)){ alert("I'm sorry. This email address seems wrong. Please" +" check the suffix for accuracy. (It should include a " +".com, .edu, .net, .org, .gov or .mil)"); return false; } alert("Verification successful! Your form would not have been submitted."); return false; } // End --> </script>

Insert this code into your BODY section

<FORM NAME="isn" ACTION="http://www.yoursite.com/cgi-bin/script.cgi" onSubmit="return emailCheck()"> <DIV ALIGN=CENTER><input type="text" NAME="email" SIZE=40 value=""><BR> <input type="submit" NAME="email1" value=" Submit "> </DIV></FORM>

Demonstration Below:

Simply Cut and Paste code snippet
Be sure to properly place script position in HEAD & BODY sections of html 

This script has been in the DesignerWiz.com Public Library.