This is what I have done so far
1. I setup a Zimbra collaboration server 8.0 in Ubuntu 12.04. FQDN of the server is abcd.com.
2. Created a forward lookup zone, A record and MX record in Windows DNS server.
3. Got a public host name from no-ip.com that should resolve to my static IP x.x.x.x. So the domain name is abcd.no-ip.com

Currently I can send emails to other domains but cannot receive emails. Now I would like to host this server on pubic Internet so that I can receive emails from other domains. What is the next step do I need to do? I am not sure about creating the MX record and all. Please help me out. Also I wish to know the port forwarding and NAT rules I need to perform on a firewall to allow my email server to communicate with other other domains. Please I need some insight.