diff --git a/README.md b/README.md
index 84452a3..41e8f7c 100644
--- a/README.md
+++ b/README.md
@@ -113,6 +113,7 @@ The following environment variables are possible for the SMTP examples.
 -	`SMTP_FROM` Sender user-part of the address. (Default: `no-reply` - e.g. no-reply@friendica.local)
 -	`SMTP_TLS` Use TLS for connecting the SMTP Mail-Gateway. (Default: empty)
 -	`SMTP_STARTTLS` Use STARTTLS for connecting the SMTP Mail-Gateway. (Default: empty)
+-       `SMTP_AUTH` Auth mode for the SMTP Mail-Gateway. (Default: `On`)
 -	`SMTP_AUTH_USER` Username for the SMTP Mail-Gateway. (Default: empty)
 -	`SMTP_AUTH_PASS` Password for the SMTP Mail-Gateway. (Default: empty)