I install zimbra here at my job, they are working ok, but only for my domain that i have registered at zimbra, for an external domain (like gmail.com) i can`t send any mail, when i try to send i receive the following message:

Message not sent; one or more addresses were not accepted.
Rejected addresses: mail@gmail.com
I think that this is some modification that i do at admins panel, but i already have saw all possible configurations and the problems persist.

someone can help-me?