i am very new to zimbra, what i need to do :

allow users to connect my zimbra mail server from outside using IMAP
i was able to connect to the server and get incoming mail but when trying to send i get the MSG that relay is not allow from this network.

my questions are :

what is the way i need to allow this.. do i need to set allow from
zmprov modifyServer zimbra.blah.co.il zimbraMtaMyNetworks ''
like the command above ??

i want to keep the server secure as possible!

thanks 4 the helpers