I think you have this email in a DB. So if you have a Email in a DB you have to select emails one by one with a LOOP and inside this loop put a code to send a email like:
http://email.about.com/cs/phpemailtips/qt/et031202.htm
http://www.php-scripts.com/php_diary/122899.php3
http://www.smartwebby.com/PHP/emailsending.asp