Relay for other mail servers

[tphan]

I am setting up Nagios server and trying to set all the alert messages will send to my zimbra server. How can I configure it in zimbra to accept the traffic. It seems It accept the the traffic without any configuration in Zimbra. So, I want it be a relay only for my nagios server and no one eles.
My zimbra is on cloud. The Nagios server is on LAN and it will send mails via the firewall then hit to the Zimbra. The firewall and the zimbra are not in the same subnet.
Please help.
Regards
tphan

[phoenix]

This question has been answered many times in the forums. If you want to send mail through a Zimbra server you should submit the mail through the correct Submission Port 587 and that will also be required to authenticate as a user.