Delete mails to a specific mail address
You need to some work here as postfix has no direct command for this.
Following sample is taken from postsuper man page:
mailq | tail -n +2 | grep -v '^ (' | awk 'BEGIN { RS = "" } { if ($8 == "[email protected]" && $9 == "") print $1 } ' | tr -d '!' | postsuper -d -
Just replace [email protected] with receiver email address.