Postmulti is great! Here are some commands I have found useful:
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####Initiate MultiInstance – this only needs to be done once
postmulti –e init
####Create Secondary Instance postfix-ses – you can use any name here instead of ‘ses’ but each instance needs an unique name
postmulti –I postfix–ses –e create
####Enable Secondary Instance
postmulti –i postfix–ses –e enable
####To view your list of postfix instances
postmulti -l
####To view the mail queue for a specific instance
postmulti -i <instance name> -x mailq
postmulti -i <instance name> -x mailq
####To manage queues
postmulti -i <instance name> -x postsuper -d ALL
postmulti -i <instance name> -x postsuper -d deferred
postmulti -i <instance name> -x postsuper -d deferred
postmulti -i <instance name> -x postsuper -d HOLD
### To Start Stop Reload and check status of instance
postmulti -i <instance name> -p <command>