$re = '/\S+?@gmail.com,\S{64}$/m';
$str = 'эта строка не подходит под описание
Почта@gmail.com,401ff14043c744fb5b10b28cfafbcf00fcffcc92e23c18b1bade7b1fdbbb0c04
эта тоже
Почта@gmail.com,daaad6e5604e8e17bd9f108d91e26afe6281dac8fda0091040a7a6d7bd9b43b5
эта_почти_подходит_но_тут_символов_не_65@gmail.com,11daaad6e5604e8e17bd9f108d91e26afe6281dac8fda0091040a7a6d7bd9b43b5
';
preg_match_all($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