Zimbra without Proxy (pre 8.5)

That’s the easy way how you can enforce https encrpytion by redirecting http to https:

su – zimbra
zmtlsctl redirect
zmcontrol stop
zmcontrol start

Works at least on Zimbra 8.0 and I think should also work on 7

Zimbra with Proxy (required from 8.5+)

With Zimbra 8.5+, a Proxy is required. This makes the configuration a little different. To configure the proxy to redirect http to https, run:

su zimbra
~/libexec/zmproxyconfig -e -w -o -a 8080:80:8443:443 -x both  -H `zmhostname`
# if your proxy is local:
zmprov ms `zmhostname` zimbraReverseProxyMailMode redirect
# if your proxy is proxy.server.name
zmprov ms proxy.server.name zimbraReverseProxyMailMode redirect
zmcontrol restart

With the latest Zimbra versions, the restart is not even necessary, it automatically detects the change within 2 minutes.

Hope this helps somebody!