The most popular out of 5 options for proxy services, is to redirect. To do this, you can run the following as zimbra user:

zmprov ms `zmhostname` zimbraReverseProxyMailMode redirect

This will redirect your URLs to the zimbra hostname based HTTPs.

Now, restart the proxy services:

su - zimbra
zmproxyctl restart

Hope this helps.

Src: https://mellowhost.com/blog/how-to-redirect-http-to-https-zimbra-8-8.html