How generate a password hash in php for iRedMail

I want to generate new passwords for all mailboxes (5000). But I dont know how the password are encrypted. Could you help me with some php  script to do this.
==== Required information ====
- iRedMail version: 0.8.1
- Store mail accounts in which backend (MySQL):
- Linux/BSD distribution name and version: Centos 6
- Related log if you're reporting an issue:
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