Which simple local mail server should I choose?

Question

Mail server

Kind time of the day
Task: to enable users to work together with some "external" mailboxes.
That is, for example, a mail service was purchased from a hoster, there is a mailbox [email protected]
The webmort there is terrible. We use Thunderbird.
It is necessary to enable "Vasya" and "Lena" to simultaneously work with [email protected]
(there are 4 such shared mailboxes, 2-3 users each).
Please suggest a not very complicated solution for this task, free of charge.
Z.Y. In the race, can someone tell me:
I installed Zimbra, but I can’t figure out how Zimbra can take mail from external [email protected] and distribute it to internal [email protected] and [email protected], as well as so that responses to external addresses from these internal boxes go via smtp. domain.ru - please help with the configuration or tell me where in Russian you can read about this
Shl. I'm watching Zimbra's wiki, but it's still hard. maybe I don’t understand what mechanisms I need and what exactly to watch
zzy. yes, I know that with my task, Zibra - from a cannon on sparrows. but this is a) out-of-the-box solution and b) general calendars and tasks and work with documents - it can very well come in handy.

Answer 1

it is necessary to pick up the mail and decompose it into local mailboxes according to some rules? fetchmail did this wonderfully, and hardly forgot how.
you can cling to the local mailer by anyone. Send exactly through it.

Answer 2

Screw it to yandex or mailru and don't worry. It's free + standard mail interface.

Answer 3

you can do this, on Zimbra set up mail.domain.ru
mail on hoster's mail set up mail forwarding from [email protected] to [email protected]
on Zimbra create users [email protected] and [email protected] .ru
share and connect to them incoming [email protected]
set up accounts for them, register from whom and the return address [email protected]