diff --git a/data/web/mta-sts.php b/data/web/mta-sts.php
index 650b8b583..74dd3b4ff 100644
--- a/data/web/mta-sts.php
+++ b/data/web/mta-sts.php
@@ -8,6 +8,17 @@ if (!isset($_SERVER['HTTP_HOST']) || strpos($_SERVER['HTTP_HOST'], 'mta-sts.') !
 
 $host = preg_replace('/:[0-9]+$/', '', $_SERVER['HTTP_HOST']);
 $domain = str_replace('mta-sts.', '', $host);
+
+// Check if domain is an alias domain and resolve to target domain
+$stmt = $pdo->prepare("SELECT `target_domain` FROM `alias_domain` WHERE `alias_domain` = :domain");
+$stmt->execute(array(':domain' => $domain));
+$alias_row = $stmt->fetch(PDO::FETCH_ASSOC);
+
+if (!empty($alias_row) && !empty($alias_row['target_domain'])) {
+  // This is an alias domain, use the target domain for MTA-STS lookup
+  $domain = $alias_row['target_domain'];
+}
+
 $mta_sts = mailbox('get', 'mta_sts', $domain);
 
 if (count($mta_sts) == 0 ||