So far I know MTA is use for sending mail...

As the stated in Zimbra Collaboration Suite Single Server Installation - Open Source Documentation...
... For sending mail, the MTA uses DNS to resolve hostnames and email-routing information. To receive mail the MX record must be configured correctly to route the message to the mail server...
If my MTA fail to install mean that I cannot send out email nor receive email...

I follow step by step the configuration that documented inside the Zimbra Collaboration Suite Single Server Installation - Open Source
[ http://www.zimbra.com/community/documentation.html ]

How can I fixed it and make the Zimbra mail server works???

This is the MTA Cross


The log during the configuration....
*** CONFIGURATION COMPLETE - press 'a' to apply
Select from menu, or press 'a' to apply config (? - help) a
Save configuration data to a file? [Yes]
Save config in file: [/opt/zimbra/config.14008]
Saving config in /opt/zimbra/config.14008...done.
The system will be modified - continue? [No] yes
Operations logged to /tmp/zmsetup.01001900-0000139009316.log
Setting local config values...done.
Setting up CA...done.
Deploying CA to /opt/zimbra/conf/ca ...done.
Creating SSL certificate...done.
Installing mailboxd SSL certificates...done.
Initializing ldap...done.
Setting replication password...done.
Setting Postfix password...done.
Setting amavis password...done.
Saving CA in ldap ...done.
Creating server entry for server.um.edu.my...done.
Saving SSL Certificate in ldap ...done.
Setting spell check URL...done.
Setting service ports on server.um.edu.my...done.
Adding server.um.edu.my to zimbraMailHostPool in default COS...done.
Installing skins...
yahoo
bones
steel
lemongrass
beach
waves
sand
lavender
sky
hotrod
bare
done.
Setting zimbraFeatureIMEnabled=FALSE...done.
Setting zimbraFeatureTasksEnabled=TRUE...done.
Setting zimbraFeatureBriefcasesEnabled=TRUE...done.
Setting zimbraFeatureNotebookEnabled=TRUE...done.
Setting MTA auth host...done.
Setting TimeZone Preference...done.
Creating domain server.um.edu.my...done.
Creating user admin@server.um.edu.my...done.
Creating postmaster alias...done.
Creating user wiki@server.um.edu.my...done.
Creating user spam.gk0eiu4g@server.um.edu.my...done.
Creating user ham.rtnzvme80@server.um.edu.my...done.
Setting spam training accounts...done.
Initializing store sql database...done.
Setting zimbraSmtpHostname for server.um.edu.my...done.
Initializing logger sql database...done.
Initializing mta config...done.
Configuring SNMP...done.
Setting services on server.um.edu.my...done.
Setting up syslog.conf...done.

You have the option of notifying Zimbra of your installation.
This helps us to track the uptake of the Zimbra Collaboration Suite.
The only information that will be transmitted is:
The VERSION of zcs installed (5.0.7_GA_2450_UBUNTU8)
The ADMIN EMAIL ADDRESS created (admin@server.um.edu.my)

Notify Zimbra of your installation? [Yes]
Notifying Zimbra of installation via http://www.zimbra.com/cgi-bin/notify...rver.um.edu.my

Notification complete

Starting servers...done.
Checking for deprecated zimlets...done.
Installing zimlets...
com_zimbra_phone
com_zimbra_url
com_zimbra_local
com_zimbra_email
com_zimbra_ymemoticons
com_zimbra_date
com_zimbra_cert_manager
done.
Initializing Documents...done.
Restarting mailboxd...done.
Setting up zimbra crontab...done.


Moving /tmp/zmsetup.01001900-0000139009316.log to /opt/zimbra/log


Configuration complete - press return to exit
Thank...