No man is an Iland, intire of it selfe; every man is a peece of the Continent, a part of the maine
— John Donne (1572-1631): Devotions Upon Emergent Occasions, 1624
It probably won't be a surprise that many Zimbra users already have an existing xmpp server, and so aren't interested in creating yet another closed chat system unconnected to the rest of the world.
One would presume that it would be possible to use the front-end nginx to redirect the incoming Zimlet xmpp connection to another xmpp server — is this is what the standalone Zimbra Chat server does? Or, does the Zimbra xmpp server that comes with Zimbra Collaboration 8.7.6 have server-to-server connection capabilities? It's kinda hard to tell, since the source links given are 404.