[mmorse]

Yup, if your able to manage the 192.168.1.2 DNS box, give it an entry for mail.mpseast.com pointing to 192.168.1.15

on the zimbra box- make sure your /etc/resolv.conf (or just see dns settings in your GUI) are set to use the internal 192.168.1.2 box for dns lookups

set your /etc/hosts to:
127.0.0.1 localhost.localdomain localhost
192.168.1.15 mail.mpseast.com mail

/etc/hostname (or again use your gui):
mail.mpseast.com

if the hostname has changed/was different-easiest to just do a fresh uninstall/reinstall of zimbra (note: you shouldn't have the proxy (perdition) service installed at all on a single server setup)

Once zimbra is fired up, be sure 'enable dns lookups' is check in both the server & global settings mta tabs (it probably will already be)

These should return the private ip's:
host -t mx domain
or
host `hostname` <-- backticks not single quotes

Later on (well you might as well set this anyway)
If you have trouble with outgoing mail & see some 554 'relay access denied' errors:
zmprov gs server.domain.com | grep zimbraMtaMyNetworks
zimbraMtaMyNetworks should have 127.0.0.0/8 192.168.1.0/24