If both servers are otherwise independant of eachother, then no. If they are part of a set of clustered servers, then the answer may be yes, but you would need both domains to exist on the same zimbra 'farm' so there would be one Zimbra instance, but multiple physical servers holding it.
This is a little outside of my realm and others here may know more, but I'm pretty sure that unless you and the other admin are ok with the basic concept, then it may be a nonstarter. Review the documents for clustering Zimbra. |