feat: Add ENV option to enable subject line logging

.env.example

@@ -31,3 +31,6 @@
 
 # Optional: This will use allow you to set a custom $mydestination value. Default is localhost.
 #DESTINATION=
+
+# Optional: This will output the subject line of messages in the log.
+#LOG_SUBJECT=yes

README.md

@@ -79,6 +79,8 @@ The following env variable(s) are optional.
 
 * `DESTINATION` This will define a list of domains from which incoming messages will be accepted.
 
+* `LOG_SUBJECT` This will output the subject line of messages in the log.
+
 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"  \

run.sh

@@ -61,11 +61,18 @@ fi
 
 #Set header tag
 if [ ! -z "${SMTP_HEADER_TAG}" ]; then
-  postconf -e "header_checks = regexp:/etc/postfix/header_tag"
-  echo -e "/^MIME-Version:/i PREPEND RelayTag: $SMTP_HEADER_TAG\n/^Content-Transfer-Encoding:/i PREPEND RelayTag: $SMTP_HEADER_TAG" > /etc/postfix/header_tag
+  postconf -e "header_checks = regexp:/etc/postfix/header_checks"
+  echo -e "/^MIME-Version:/i PREPEND RelayTag: $SMTP_HEADER_TAG\n/^Content-Transfer-Encoding:/i PREPEND RelayTag: $SMTP_HEADER_TAG" >> /etc/postfix/header_checks
   echo "Setting configuration option SMTP_HEADER_TAG with value: ${SMTP_HEADER_TAG}"
 fi
 
+#Enable logging of subject line
+if [ "${LOG_SUBJECT}" == "yes" ]; then
+  postconf -e "header_checks = regexp:/etc/postfix/header_checks"
+  echo -e "/^Subject:/ WARN" >> /etc/postfix/header_checks
+  echo "Enabling logging of subject line"
+fi
+
 #Check for subnet restrictions
 nets='10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16'
 if [ ! -z "${SMTP_NETWORKS}" ]; then