TheFrenchCommander

Found the solution. It wasn’t “mail2” but “mail_2”:

$mail2 = $wpcf7->prop('mail_2');
$mail2['body'] = str_replace("[rfq-code]", $submited['posted_data']['rfq-code'], $mail2['body']);
// Save the email body
$wpcf7->set_properties(array("mail" => $mail,"mail_2" => $mail2));
return $wpcf7;