Warning in Plesk Premium Email: This domain is configured for Plesk Premium Email - Free, but should not

Symptoms

A license was installed for the paid Plesk Premium Email version, however, the following warning is shown in Plesk Premium Email:

PLESK_WARN: This domain is configured for Plesk Premium Email - Free, but should not

Cause

Plesk Premium Email - Free permission is enabled at Subscriptions > example.com > Customize > Permissions 

Resolution

1. Log into Plesk
2. Go to Subscriptions > example.com > Customize > Permissions.
3. Disable Plesk Premium Email - Free.
4. Click OK

Note: If the option is not enabled try to enable/disable it to re-apply the settings.