Not the end of the world, however you should edit /etc/hosts at some stage and add the full name of your server after the word localhost ( a space between localhost and the name is good).
e.g. 127.0.0.1 localhost myserver.mydomain.com

There may well be a line below that with the IP address of the machine together with the machine name.
e.g.

192.168.0.1 myserver

and ideally that should be

192.168.0.1 myserver.mydomain.com myserver

None of that is anything other than dotting i's and crossing t's, and can wait till we are done.

There is a file in /etc/postfix/ called master.cf Near the top is a line that should read something like

smtp inet n - - - - smtpd

This tells Postfix that for smtp port 25 it must use the secure authentication daemon. You want to duplicate that line on a new line immediately below that but replace the smtp with the port number 587
i.e.

587 inet n - - - - smtpd

and save the file.

I have also seen comments that uncommenting the line immediately below the smtp line (the one starting submission - remove the #) will do the same thing.

You will then need to restart Postfix,

/etc/init.d/postfix restart

and try sending email from ZC admin, then post the mail log.

We may well have to do some DNS edits and fixup to make everybody happy, but we're getting closer