I have 4 different sites containing users.

Lets say sites : A, B , C and D.

I want to have one server per site with all the services so if my link is broken between two sites it stills works.

Is it possible with Zimbra ?

I feel it should be possible for messaging and directory but I am not sure about calendar ...

And if yes ... can user a from A organize a meeting with a user c from C and d from D... can the servers communicates to find freebusy information ... and which protocol is used between servers.

Thanck you for any information

PS : I had a look at the documentation about multi-server but I didn't understand for sure if it means multi-server with different services on each (directory, MTA, etc ...) or different servers with each all the services on.