Plesk does not send notification when usage limits are exceeded for a domain with "Overuse" option enabled.
Notify me by email in cases of overuse check box tab is unset.
Select "Notify me by email in cases of overuse" checkbox at Home > Service Plans > [ServicePlan] > Resources and click Update & Sync button to apply the setting to assigned subscriptions:
For a single subscription it can be set at Plesk > Subscriptions > example.com > Account pane > Customize > Resources tab.
"me" in "Notify me by email in cases of overuse" option refers to the user who is exceeding the limit.