Linux can handle multiple IP's on one interface using virtual interfaces.

And it would be very easy to have zimbra working on one interface and lets say, your apache on another interface.

But zimbra always binds itself to all available interaces. This makes it very difficult to have any other apaches/sendmails/postfixes running on the same host with zimbra. Some people consider this as bug and there is a bug-report about this with 56 votes already:

Bug 6111 – allow user to specify interface to bind to, instead of taking them all.

56 is quite high and if some people vote for this bug too, it might actually be considered in the next release.

Technically its quite simple to bind zimbra only to one interface, but there are many different tools in the zimbra-suite involved and one has to change every config for every networking-program in zimbra. And every update will rewrite this configs again. It would be much easier if zimbra would do it by itself. If you agree with that please consider voting for the above bug.

To the OP: I think this wiki is outdated