$re = '/(?i)(?>.*?)(nugenix|cialis|somethingelse)(?>.*?@)(?!.*?(nugenix|cialis|somethingelse))/';
$str = '// Match
Return-Path: <get-some-nugenix-for-health@whatever.yooooo.com>
Return-Path: <get-some-nugenix@-sakana15.com>
Return-Path: <nugenix-for-health@-sakana15.com>
<anycharacters+somethingelse+anyothercharacters+@
// No match - Banned words in Sender and Domain
Return-Path: <get-some-nugenix-for-health@whatnugenixever.yooooo.com>
Return-Path: <get-some-nugenix-for-health@nugenixwhatever.yooooo.com>
Return-Path: <get-some-nugenix-for-health@whatever.yooooo.comnugenix>
Return-Path: <get-some--for-healthnugenix@whatnugenixever.yooooo.com>
Return-Path: <nugenixget-some-for-health@nugenixwhatever.yooooo.com>
// No Match - Banned words only in domain
Return-Path: <get-some-for-health@whatever.yooooo.com>
Return-Path: <get-some-for-health@nugenixwhatever.yooooo.com>
Return-Path: <get-some-for-health@whatevernugenix.yooooo.com>
Return-Path: <get-some-for-health@whatever.yooooo.comnugenix>';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php