I am planning to deploy on-premises ZCS FOSS into my small business scenario. At this point I have few doubts in my mind (might not fully relevant with zimbra) need to rectify.

1. At present our mails are hosted on Service Provider's server. I understand that, after setting up ZCS for the same domain, alongwith setting up mx priority for ZCS, mails from outside shall come to ZCS server. My question is: during setting up the things, for any particular incoming mail, if recipient not found on my Zimbra server, will it be delivered to 2nd mx priority i.e. hosted servers?

2. As being small business, we do not have redundant internet connectivity. By any means, if connectivity fails, what shall happen to incoming mails? means, shall they be waiting for server to become available? in other words, how much time usually mail stays in queue at senders server?

3. I understand that I can use Zimbra for more than one domain. Can I create different administrator for each domain?

Thanks in advance.