Build multi-arch container images across stack
diff --git a/apps/maddy/auth/Dockerfile b/apps/maddy/auth/Dockerfile
index 3b1168d..342f121 100644
--- a/apps/maddy/auth/Dockerfile
+++ b/apps/maddy/auth/Dockerfile
@@ -1,3 +1,6 @@
 FROM giolekva/maddy:v0.4.4
 
-COPY auth-smtp /usr/bin/auth-smtp
+ARG TARGETARCH
+
+COPY auth-smtp_${TARGETARCH} /usr/bin/auth-smtp
+RUN chmod +x /usr/bin/auth-smtp