[Web] Allow aliases as send-as

data/web/mta_sts.php

@@ -0,0 +1,18 @@
+<?php
+error_reporting(0);
+header('Content-Type: text/plain');
+
+echo $_SERVER['HTTP_HOST'];
+
+foreach (dns_get_record('mailcow.email', DNS_MX) as $mx_r) {
+  $mx_s[] = $mx_r['target'];
+}
+
+!empty($mx_s) ?: exit();
+
+echo 'version: STSv1' . PHP_EOL;
+echo 'mode: enforce' . PHP_EOL;
+foreach ($mx_s as $mx_r) {
+  printf('mx: %s' . PHP_EOL, $mx_r);
+}
+echo 'max_age: 86400' . PHP_EOL;