diff --git a/src/postfix/Containerfile b/src/postfix/Containerfile
index 43f9364..260532a 100644
--- a/src/postfix/Containerfile
+++ b/src/postfix/Containerfile
@@ -23,7 +23,7 @@ ARG FILESUID=5000
 ARG DEBIAN_FRONTEND=noninteractive
 
 # set the mailname
-echo "mail.brbytes.org" > /etc/mailname
+RUN echo "mail.brbytes.org" > /etc/mailname
 
 # install packages we want
 RUN apt update -y && apt install -y postfix dovecot-imapd dovecot-lmtpd
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