How to set limitations on outgoing email messages in Plesk
To manage limitations on outgoing email messages, first log in to Plesk and enable the option Switch on limitations on outgoing email messages at Tools & Settings > Mail Server Settings and click OK to apply the changes.
To monitoring the outgoing mail, go to Tools & Settings > Outgoing Mail Control:
The General tab shows the number of Plesk objects that have attempted to exceed limits.
To see the detailed report about a certain Plesk object, go to the corresponding tab - Email Addresses, Domains or Subscriptions - and click the required object.