Some queries on iRedMail

==== Required information ====
- iRedMail version: 0.8.7
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): LDAP
- Linux/BSD distribution name and version: RHEL 7
- Related log if you're reporting an issue:
====

I want to propose iRedMail with iRedAdmin-Pro to company.  There are some queries that I have to clarify first as listed below.

1. My company has serveral subsidiaries using same domain name.  I want to separate them by ou on LDAP.  May I create different ou by iRedAdmin-Pro and manage them?

2. May I configure staff ID as login name instead of mail address?

3. Does vacation enable on iRedAdmin-Pro instead of on WebMail by user?

4. Does iRedMail support High Availability?

Thanks & Best Regards