If you need to get your Plesk users’s password, the information is stored in a database named psa and in a table named accounts. The passwords are not hashed, they are only stored as BLOBs in Plesk 10 or later (previous versions were clear text) so a simple CONVERT can list them.
Start mysql and prompt for password. Then select database to use.
mysql -p mysql> use psa
Run the query (Plesk 10)
SELECT a.id, CONCAT(m.mail_name,"@", d.name) AS email_address, CONVERT(a.password USING utf8) AS password FROM mail m LEFT OUTER JOIN domains d on d.id=m.dom_id LEFT OUTER JOIN accounts a ON a.id=m.account_id
Optionally, you can add the following search criteria
WHERE d.name IN ('domain1.com','domain2.com')
References: