diff --git a/README.md b/README.md
index d3de115..52cb677 100644
--- a/README.md
+++ b/README.md
@@ -33,7 +33,7 @@ The following env variables need to be passed to the container:
 * `SMTP_PASSWORD` Password of the SMTP user.
 * `SERVER_HOSTNAME` Server hostname for the Postfix container. Emails will appear to come from the hostname's domain.
 
-To use this container from anywhere, the 25 port needs to be exposed to the docker host server:
+To use this container from anywhere, the 25 port or the one specified by `SMTP_PORT` needs to be exposed to the docker host server:
 
     docker run -d --name postfix -p "25:25"  \ 
            -e SMTP_SERVER=smtp.bar.com \