Is it possible to enable Plesk Premium Email (Kolab) for specific email accounts?
Currently, there is no way to enable Plesk Premium Email (Kolab) for a a particular email account.
If you would like to see this functionality in Plesk, please vote for it on Plesk UserVoice:
As a workaround, enable Plesk Premium Email for specific subscriptions:
Create a new service plan in the Service Plans menu.
Enable Plesk Premium Mail for this service plan in the Permissions settings.
Assign subscriptions to the service plan (no more than X email accounts in total depending on a Plesk Premium Email license).