I want to allow a couple of mail servers from my work to relay through my Zimbra mail server. I assume that the correct place to do that is in the MTA tab for my server and adding the IP's to the "MTA Trusted Networks" entry.

(Please correct me if I'm wrong).

In doing so, the mail that I am sending through it is sometimes marked as SPAM with such a high score that it is discarded. How do I bypass the SPAM filter for allowed relays?