add this to adduser.php around like 49 or 50 after it check to see if there is a username and email but before it checks the db to see if the username is registered
// ------------------------------------------------------------
// checks email format
if(!ereg("^([0-9,a-z,A-Z]+)([.,_]([0-9,a-z,A-Z]+))*[@]([0-9,a-z,A-Z]+)([.,_,-]([0-9,a-z,A-Z]+))*[
.]([0-9,a-z,A-Z]){2}([0-9,a-z,A-Z])?$",$Email)){
$html -> not_right("$lang[BAD_EMAIL2]",$Cat);
}
aslo add BAD_EMAIL2 to the adduser.php for the default language of your board in tle languages directory
btw i got the email validation code from the link below i think its pretty good i think its public domain there is an explantion of it here
http://devhome.net/php/tips/4.html
