<?php
 
$mailRegExp = '/
    ([a-zA-Z0-9-_.\\+]+)
    @
    ([a-zA-Z0-9-]+\\.)?
    ([a-z0-9-]+)
    (\\.[a-z]{2,4})+
/x';
$string = "Пешите нам на электронку masha_666@hot.mail.com.tw, donotreply+dasha-sexxy@habr.com и admin@internet.org";
preg_match_all($mailRegExp, $string, $matches, PREG_SET_ORDER);
 
echo "В тексте обнаружены следующие электропочты:\n";
foreach ($matches as $mail) {
    echo "{$mail[0]}\n";
}

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