I've no idea how why it worked before as I don't know what you did to DNS or Zimbra during or after the install to make it work. You din't really provide much information about whether this was a new install an upgrade nor how long the server has been running and nothing from the
log files. It helps to see some error messages and/or diagnostic information as that will give a more accurate picture of the problem they're experiencing.
I don't know if you've seen this but openSUSE will no longer be supported after the current 5.x series of ZImbra - that means no binary builds will be available.
The problem you've currently got is that Zimbra (postfix) can't find the IP address of the server, hence the 'MTA transport...' error. You do not use localhost & the domain name for the Zimbra server (in the hosts file) as you would have seen in the link I gave you, it should be a valid LAN IP & the FQDN of your server and you need a local DNS server to resolve that address.
I would have thought the fact you're having problems with YaST to be unrelated to the Zimbra problem.