- print_r: documentation ( source)
- preg_match_all: documentation ( source)
<?php
$text = 'input class="email border-radius text-center" type="email" placeholder="Your email" value="francof.isd@tutanota.com"';
preg_match_all("/[._a-zA-Z0-9-]+@[._a-zA-Z0-9-]+/i", $text, $matches);
print_r($matches[0]);