technical docs about iRedmail

==== Required information ====
- iRedMail version:
- Store mail accounts in which backend (LDAP/MySQL/PGSQL):
- Linux/BSD distribution name and version:
- Related log if you're reporting an issue:
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Hi.
First I thank you for all your efforts to make iRedmail like it looks today.
I want to ask if there is any technical docs about the internel works of this server (database tables and fields meanings ....).
And do you permit for people to do forks from your project.
Thank you.