Zimbra mailbox install, nomenclature

[number9]

We have a multi-server setup in which we have two MTA boxes (MTA01 MTA02) and one Mailbox (mailbox01). We are bringing up another mailbox (mailbox02), but it has been quite some time since we installed Zimbra, so I have a nomenclature question regarding the install, among other things.
Note, I walked into this setup, I did not set all of this up originally.

This is Zimbra Network Edition 5.0.23, RHEL 64 bit.

Going through the initial setup (mailbox02), under the menu "store configuration", SMTP host
is UNSET. Ok, according to the docs I set this to be the MTA...
From the docs: "This is the mta-server host name." Which one? We have two MTAs,
but I read that I can not (easily) set them up as failovers. In fact when MTA01 goes
down, MTA02 just sits there, but that is another matter.

If I look through my current mailbox settings, on mailbox01 I see: zimbraSmtpHostname: localhost

If I grep for any MTA in the current config on mailbox01 I see:
zimbraMtaMyDestination: localhost
zimbraMtaRelayHost: my final destination mailer, not Zimbra

So I am a bit confused. Do I set the SMTP hostname to be localhost, one of the MTAs or my final destination (we have another server which actually mails to the internet).

Any help getting this straight would be appreciated.

Thanks.