general postfix query

[padraig]

if zimbra is down for some length of time ~24hrs. what happen to the in-comming e-mail
are they re-queued externally & if so when will you get the e-mails for the missing day the server was down

[mmorse]

Well it's not really a postfix question because you don't know what the other end is running - no hard rule but most email servers retry delivery for 24-96hrs. There aren't many solutions that have their defaults set to just 1 day, because they realize that something could go wrong over a 3day weekend for example.

Ever send someone a message, then get the postmaster message back with something like: 'Their mailserver seems to be currently unreachable, but we will retry delivery approx _ times over the next 72 hours.'

You can setup a backup MX record mta -another zimbra box will do - to hold everything until your primary comes back online.
The MX record with the smallest preference number has the highest priority and is the first server to be tried, so it doesn't affect normal delivery when your main server is online.

You can also use multi-server setups for redundancy & clustering for high-availability of the mailstores.
NE: RHEL & RHCS (which I see you are ZCS Version: 4.5.6_GA_1044.RHEL4_64_20070706134444 RHEL4_64 NETWORK)
Check your support portal for the documentation.

Other methods:
Typical FOSS method: DRBD & Heartbeat [SOLVED] Zimbra on DRBD
There's also: http://www.zimbra.com/forums/install...o-cluster.html