Comment 5 for bug 378955

... in the past version of Nexenta you had to run perl -pi -e 's/hash/dbm/g' /etc/postfix/main.cf .. or to change
the defaults of alias_database and alias_maps from hash to dbm by hand after the install was done ...

..., but that doesn't seems to be the case now since you are not getting the hash error --- I guess that was fixed in this new version of Nexenta.

---
Postfix is now set up with a default configuration. If you need to make
changes, edit
/etc/postfix/main.cf (and others) as needed. To view Postfix
configuration
values, see postconf(1).

After modifying main.cf, be sure to run '/etc/init.d/postfix reload'.

Running newaliases
postalias: fatal: dict_mkmap_func: unsupported dictionary type: hash:
Is the postfix-hash package installed?
dpkg: error processing postfix (--install):
 subprocess post-installation script returned error exit status 1
Processing triggers for man-db ...
Errors were encountered while processing: postfix