If you find yourself working with a new client who only has a Plesk backup file to work with and wants you to create mailboxes on a new server keeping their old usernames and passwords, it can be a bit of a hassle to find the usernames and passwords for the mailboxes they have used. Luckily all this information can be found in the expanded backup itself in a file with this format
Get a clean list of usernames and passwords
To get a clean list of mailbox users and passwords you can use following PHP code in the expanded backup folder. This works with backups created in Plesk Onyx 17.5.3.