I want to set up a ZCS 7.1.3 network edition system with four servers. Two of the servers, the central directory server for ZCS and other applications and the mailstore server, should be in a private network with private RFC 1918 IP addresses and a DNS server for the private network. The other two servers, one MTA handling incoming and outgoing emails and one proxy server for web and IMAP proxying, should have official IP addresses with worldwide resolvable names. Between the two networks there is a packet filtering firewall with two interfaces which NATs the internal network. All in all I have:

Private network with:
- Directory server (, ds.mydomain.pri)
- Mailstore server (, ms.mydomain.pri)

Paket filtering firewall

Official network with:
- Mail exchange server (mx2.mydomain.de)
- IMAP/HTTP proxy server (comms.mydomain.de)

Now, the problem is that I can not make the external proxy server talk to the internal mailstore server. Web proxying does not work, nginx gives a "bad gateway" message.

I have a case open at Zimbra with this question but maybe someone here can help. I do not think that my setup is something special so it must be possible somehow.

Does someone have a similar setup and could give me some configuration hints?

Thank you.