The following script helps the admin to activate a relayhost in postfix configuration. It asks the user for the values on command line and inserts those values into postfix configuration

#!/bin/sh
 
main='/usr/syno/mailstation/etc/main.cf'
#main='./main.cf'
#map='./smtp_auth'
map='/usr/syno/mailstation/etc/smtp_auth'
echo -n 'Hostname of relayhost:  '
while read relayhost
do
 [ "x$relayhost" != 'x' ] && break
 echo -n 'Hostname of relayhost:  ' && continue
done
 
echo -n "set $relayhost as relay (r) or fallback (f)? Default f:  "
while read type
do
 case $type in
  'r' | 'f')
  break
  ;;
  *)
   type='f'
   break
  ;;
 esac
done
 
echo -n "Username for login on ${relayhost}:  "
while read user
do
 [ "x$user" != 'x' ] && break
done
 
if [ "x$user" != 'x' ]
then
 echo -n "Password of $user @ $relayhost: "
 while read passwort
 do
  break
 done
fi
 
for i in relayhost smtp_sasl_auth_enable smtp_sasl_password_maps smtp_sasl_security_options smtp_use_tls smtp_enforce_tls smtp_tls_enforce_peername
do
 case $i in
  'relayhost')
        [ "$type" == 'f' ] && echo 'fallback_relay = '$relayhost >> $main
        [ "$type" == 'r' ] && echo 'relayhost = '$relayhost >> $main
  ;;
  'smtp_sasl_auth_enable' | 'smtp_use_tls' | 'smtp_enforce_tls')
        echo "$i = yes" >> $main
  ;;
  'smtp_sasl_password_maps')
        echo "$i = $map" >> $main
        echo "$relayhost ${user}:${passwort}" >> $map
        /usr/syno/mailstation/sbin/postmap $map
  ;;
  'smtp_sasl_security_options')
        echo "$i = noanonymous" >> $main
  ;;
  'smtp_tls_enforce_peername')
        echo "$i = no" >> $main
  ;;
  *)
        continue
  ;;
 esac
done