My question is about the configuration of a email system in odoo and the effect of this configuration.

My use case is this one :

X workers, each one with a professional e-mail adress

I want to centralize the communications with customers and leads, to keep or increase the quality (I want to keep the history of the relations in a centralized way to be aware about every things and to share more easily informations)

I dont understand how odoo works and so, dont understand how to configure it.

For example : 

what is a alias domain in the Odoo context ? Is it a FQDN? or, is it what ever we want?

What is the better manner to configure the servers ? Is it necessary or better to configure a specific mail server (in/out going) for Odoo?

How to be sure that all mail will be in Odoo even if the message comes on the professional box, and even if answer is made from that one? How to be sure, also, that "private" or "confidential" messages will keep private or confidential? How to communicate the change with customers?

Do you have any experience in deployment of this solution, and the way to manage this change?