Connect to your database - server, using the database "PSA":
plesk db
Query the PSA - database with for example:
SELECT domains.id, domains.name AS DOMAIN_NAME, mail.mail_name AS eMail_ADDRESS_NAME, Limits.value AS DOMAIN_quota, mail.mbox_quota AS MBOX_quota from Limits, clients, domains, mail, Subscriptions, SubscriptionProperties WHERE mail.postbox='true' AND limit_name = 'mbox_quota' AND mail.dom_id = domains.id AND clients.id = domains.cl_id AND Subscriptions.id=SubscriptionProperties.subscription_id AND Subscriptions.object_type='domain' AND object_id=domains.id AND SubscriptionProperties.name = 'limitsID' AND SubscriptionProperties.value = Limits.id ORDER BY domains.name ASC;