I was told that Zimbra doesn't support modifying nginx to support this and that it would probably be simpler and easier to setup a manual redirect to a mail store. Here is how I quickly achieved this on my Ubuntu proxy node
apt-get install lighttpd
edit your /etc/lighttpd/lighttpd.conf file. Here's a diff between the stock and my modified one. This conf will take ANY request on port 7071 and redirect to
https://zimbra.mailstore.com:7071/zimbraAdmin/ Code:
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< "mod_redirect",
---
> # "mod_redirect",
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< server.port = 7071
---
> # server.port = 81
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< url.redirect = ( "^.*$" => "https://zimbra.mailstore.com:7071/zimbraAdmin/" )
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< ssl.engine = "enable"
< ssl.pemfile = "/etc/lighttpd/certs/lighttpd.pem"
Lastly you will want to install your cert. I have a commercial cert on my proxy so I made a copy like this
mkdir /etc/conf/lighttpd/certs
cat /opt/zimbra/ssl/zimbra/commercial/commercial.key >/etc/conf/lighttpd/certs/lighttpd.pem
cat /opt/zimbra/ssl/zimbra/commercial/commercial.crt >>/etc/conf/lighttpd/certs/lighttpd.pem
/etc/init.d/lighttpd restart and you should be in business.