$re = '/^ActiveCampaign\/email/m';
$str = 'activecampaign/email/dp philippines newsletter 10apr2019
ActiveCampaign/email/The Cube Pattaya TH-EN ALL 22AUG19/Luxury Condo Development in Pattaya, Thailand
ActiveCampaign/email/Samui Beachfront Villas TH-EN Group TH-EN MAY19 (Tide Samui)/Beachfront Villas in Koh Samui with Private Pool';
preg_match_all($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