If im thinking about the average zimbra admin, its a person that do not have time or the knowledge to tweak all the aspects of the server and thus he mind end up to situation i did (and i do have time, i was just a bit careless) - So, it would make sense that the installation procedure would check what hostname ends up in the smtp server.
There are two basic types of detections that land an IP in this page. RFC2821 section 220.127.116.11 says that there are only two legal types of HELO/EHLO a mail server can issue - either a fully qualified domain name (eg: "mail.example.com") or an "IP literal" (eg: "[18.104.22.168]").
For example, default fedora installation advertises "localhost.localdomain" as its default hostname, with minimum installation in zimbra, this will be used as helo/ehlo string in postfix and eventually gets the zimbra host system blacklisted by CBL. More info on the matter: http://cbl.abuseat.org/namingproblems.html