I had the problem, that the installation program always terminated with the messages, my /etc/host is wrong.
I had a look and indeed the line with my server was
IP HN FQHN
I changed this to
IP FQDN HN
but this still didn't work.
After some trial and error I found out, that the installation procedure assumes
*all* lines in the host file in the given order, even for hostname without interest for Zimbra.