diff --git a/.env.production.sample b/.env.production.sample
index 0759ed7fa..28afee246 100644
--- a/.env.production.sample
+++ b/.env.production.sample
@@ -42,6 +42,7 @@ SMTP_PORT=587
 SMTP_LOGIN=
 SMTP_PASSWORD=
 SMTP_FROM_ADDRESS=notifications@example.com
+#SMTP_DOMAIN= # defaults to LOCAL_DOMAIN
 #SMTP_DELIVERY_METHOD=smtp # delivery method can also be sendmail
 #SMTP_AUTH_METHOD=plain
 #SMTP_OPENSSL_VERIFY_MODE=peer