might work now

rootfs/etc/service/postfix/run

@@ -1,5 +1,70 @@
 #!/bin/bash
+POSTFIX='/usr/sbin/postfix'
+MONITOR_INTERVAL=10 # seconds
 
-echo "postfix starting..."
+exec 2>&1
 
-exec /usr/lib/postfix/master
+if [[ ! -d /state/envdir ]]; then
+    mkdir -p /state/envdir
+    chown mastodon:mastodon /state/envdir
+fi
+
+if [[ ! -e /state/envdir/WEB_DOMAIN ]]; then
+    if [[ -n "$WEB_DOMAIN" ]]; then
+        echo "$WEB_DOMAIN" > /state/envdir/WEB_DOMAIN
+    else
+        hostname --fqdn > /state/envdir/WEB_DOMAIN
+    fi
+    chown mastodon:mastodon /state/envdir/*
+fi
+
+cat /etc/postfix/main.cf | grep -v '^myhostname' > /etc/postfix/main.new
+rm /etc/postfix/main.cf
+echo "myhostname = $(cat /state/envdir/WEB_DOMAIN)" >> /etc/postfix/main.cf
+echo "myorigin = $(cat /state/envdir/WEB_DOMAIN)" >> /etc/postfix/main.cf
+cat /etc/postfix/main.new >> /etc/postfix/main.cf
+rm /etc/postfix/main.new
+
+running() {
+  pkill -0 master
+}
+
+start() {
+  echo "postfix starting..."
+  /etc/init.d/postfix start
+}
+
+stop() {
+  if running; then
+    echo Stopping
+    /etc/init.d/postfix stop
+  fi
+}
+
+reload() {
+  echo Reloading
+  /etc/init.d/postfix reload
+}
+
+check() {
+  echo Checking
+  "$POSTFIX" check
+}
+
+status() {
+  "$POSTFIX" status
+}
+
+
+trap 'echo INT; stop; exit' INT
+trap 'echo QUIT; stop; exit' QUIT
+trap 'echo TERM; stop; exit' TERM
+trap 'echo STOP; stop' STOP
+trap 'echo HUP; reload' HUP
+trap 'echo USR1; check' USR1
+trap 'echo USR2; status' USR2
+
+while :; do
+  running || start
+  sleep $MONITOR_INTERVAL
+done