Is it possible to set outgoing mail limit for local emails so that emails sent between mailboxes on the same server are also limited according to outgoing limit control settings?
Outgoing mail control can be applied only to email addresses, domains or subscriptions. It applies to all outgoing mails sent to external servers. It is not possible to limit emails sent locally (between mailboxes stored on the same server).
Described functionality can be considered as a feature request on Plesk User Voice portal: https://plesk.uservoice.com/forums/184549-feature-suggestions