diff --git a/Dockerfile b/Dockerfile
index 35d5771..90a138d 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -49,6 +49,8 @@ ARG NEXT_PUBLIC_UMAMI_SRC=""
 ARG NEXT_PUBLIC_UMAMI_ID=""
 ENV NEXT_PUBLIC_UMAMI_SRC=$NEXT_PUBLIC_UMAMI_SRC
 ENV NEXT_PUBLIC_UMAMI_ID=$NEXT_PUBLIC_UMAMI_ID
+ARG SMTP_USER=""
+ENV SMTP_USER=$SMTP_USER
 # Shared session cookie across www.* and app.*. Needed at build time too: process.env is
 # inlined into the Edge middleware bundle, so a runtime-only value would leave the
 # middleware and the route handlers disagreeing about the cookie scope.