Usually the blacklists care about the HELO name you give on your outgoing connections, not the incoming one. Usually Zimbra's postfix will figure it out automatically from the name of your machine (you do have you machine set to its real hostname, right?)
It is possible to override the name that it uses though.
Code:
zmlocalconfig -e postfix_smtp_helo_name=your.domain.name
You may need to restart configd and the mta after changing that for it to pick it up.