You can get the plesk admin password from the file /etc/psa/.psa.shadow

1. login to mysql

mysql -u admin -p

2. select the database psa

use psa;

3. Run the mysql query that will give login details of each mailbox under a specified domein

select m.mail_name, m.password,d.name  from mail m, domains d where m.dom_id = d.id and d.name =’supportpro.com‘;

If you require help, contact SupportPRO Server Admin