diff --git a/plinth/modules/email_server/data/etc/dovecot/conf.d/05-freedombox-auth.conf b/plinth/modules/email_server/data/etc/dovecot/conf.d/05-freedombox-auth.conf
index b8b027b42..4d3cb8e22 100644
--- a/plinth/modules/email_server/data/etc/dovecot/conf.d/05-freedombox-auth.conf
+++ b/plinth/modules/email_server/data/etc/dovecot/conf.d/05-freedombox-auth.conf
@@ -12,6 +12,15 @@ passdb {
   result_success = return-ok
 }
 
+userdb {
+  # UID number lookup (10001@example.com)
+  driver = ldap
+  args = /etc/dovecot/freedombox-ldap-userdb-aliases.conf.ext
+  result_failure = continue
+  result_internalfail = return-fail
+  result_success = return-ok
+}
+
 userdb {
   driver = ldap
   args = /etc/dovecot/freedombox-ldap-userdb.conf.ext