starting zimbra mail server

[rags]

Hi all,
I want to start with zimbra mail server installations and create users.
But I don't know much about zimbra mail server.

My plan os starting is as:-

1) Installation of zimbra mail server.

2) Create new users.

3) verify end to end mail communications by sending mail from user1 to user2.

Doubts:-
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1) Can I create my domain inside my office, office will be having their own domain and proxy.

2) Can I send and receive mails from open cloud like yahoo.com, gmail.com etc and from private network like ibm.com, accenture.com etc