Openchange server without AD?

Question

Active Directory

Good day.
Background.
Delivered iRedMail (PgSql) + Sogo. In office of 95% of Thunderbird - there all by way.
But there are 5% of users who have Outlook. So here it is necessary that the general calendars and contacts are everywhere ...
Well, after googling, I understand that either exchange or alternatives.
Of the alternatives, it seems like a working OpenChange Server (is there more?) + sogo-openchange.
And here are the questions:

1. OpenChange can work without AD? because iredmail has authorization in pgsql.
   
2. Is it important that the domain is conditionally example.net, and the mail is @mydomain.ru ?
   and it turns out that it seems like you need to configure OpenChange in AD (well, I mean in samba) for authorization, but I don’t understand the point, because users generally lie in the SQL database and the domain is different ...
   

PS: I was lucky, I didn’t see exchange live, I didn’t use it

Answer 1

Put those 5% - thunderbird, I think it will be much easier than to fence all sorts of crutches (this is if there is no money), or buy and install Exchange. Why this unsupported configuration, pain for the next admin? (and myself too)