Well, I tried shared folder from the GUI and I did it with success (thanks alexkelly for your instructions), but I found that Shared Folders is not what I'm looking for, because Shared Folders allows a user to see emails from this common accounts like
info@mydomain.com.ar but it doesn't allow to create and send a new email using this common account.
As for testing share folders using GUI, I had to create a user for the common account, and after I found that Shared Folder is not what I need for my company, then I took advantage of the common created account
info@mydomain.com.ar and I tried to add as external account for the test user I created (santiago@mydomain.com.ar).
Doing that, I discovered that when I log as this test user, I can read the info@ inbox, and I also can send mails using info@ account, I also have the contacts, calendar, etc, etc.
The only problem with this method, is that it's the user responsability to choose the account from which he/she wants to send the email. Zimbra doesn't recognize that if the user is standing at info@ inbox or outbox and press the New Mail button the account from which the mail has to be send it the info@ and not the default user account.
Another thing I don't like very much about this, it's that I don't see a solution to the problem that we're having now at the office with IMAP account shared, that is if one user sends an email from the info@ account and the user doesn't sign it at the end, the recipient sees that the mail it's sent from info@ and nothing else, so it cannot know which person of the office sends the email. That's why I asked in my first post, if it's possible with common accounts that for example my test user sends an email using info@ common account and the email's envelope goes out with something in the header saying: "santiago@mydomain.com.ar in the name of
info@mydomain.com.ar", so the recipient could know which person of the office sent the email using the common account.
Perhaps all the things I mentioned have a solution in Zimbra, but as I'm a newbie I really don't know, although I'm still investigating reading a lot from this forum, wiki and googleing.
If someone is using common accounts in the way I described, and want to post his/her experience, I think it'll be useful to me.
Thanks in advance.