We have wanted to do a zimbra (looked at all versions) a hosted mail solution for many years. Always afraid to jump in and go for it on the open version or couldn't because of cost on the enterprise. We have provided a hosted exchange (possible with our Microsoft partnership). However we would like to bring a more affordable hosted email to our clients and for sure are NOT fans of microsoft would like to do a zimbra solution. The question is what is really envolved to make the open zimbra client ready for a multi-tenant hosted environment? We unfortunately for the goals of this project cant budget the paid versions but would like to bring the core features of what people expect on a hosted email. That in mind what is really entailed to make the open version ready and working for end users?

As a side note we will be using Djigzo as well but that's really a separate issues for the most part.