Spam issues while using Postfix as a two-way relay

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http://serverfault.com – I want to use a Postfix box to do two things: Relay mail from any host on the internet addressed to one of my domains to my Zimbra server Relay mail from my Zimbra server to any address on the internet. To try and accomplish this I have configured Postfix thusly: mynetworks =, zimbra_ip/32 myorigin = zimbra_server mydestination = localhost, zimbra_server relay_domains = example.com example.org transport_maps = hash:/etc/postfix/transport_map local_transport = error:no mailboxes on this host transport_map looks like this: example.com smtp:[zimbra_server] example.org smtp:[zi (HowTos)