I'm newbie in this. Please tell me what line of CODE I need in my main.cf file to be able to SERVE MULTI DOMAINS and be able to SEND/RECEIVE mail from anywhere using mail clients such as outlook, etc. Here is the code in the main.cf file that work only with 1 domain and be able to only receive mail from anywhere:

command_directory = /usr/bin
daemon_directory = /usr/libexec/postfix
myhostname = hostname.domainname
mydomain = only1domain_listed_here
myorigin = $mydomain
inet_interfaces = all
mydestination = $mydomain, $myhostname, localhost.$mydomain
mynetworks = 111.222.333.444, 127.0.0.0/8 note: my ip without slash+number
relay_domains = $mydestination
alias_maps = hash:/etc/postfix/aliases
debug_peer_level = 2
debug_command =
PATH=usr/bin:usr/X11R6/bin
xxgdb $daemon_directory/$process_name $process_id & sleep 5

sendmail_path = /usr/sbin/sendmail.postfix
newaliases_path = /usr/bin/newaliases.postfix
mailq_path = /usr/bin/mailq.postfix
setgid_group = postdrop
manpage_directory = /usr/share/man
sample_directory = /usr/share/doc/postfix-1.1.11/samples
readme_directory = /usr/share/doc/postfix-1.1.11/README_FILES
alias_database = hash:/etc/postfix/aliases.db
notify_classes = resource, software, bounce, policy

Please help me out... I have tried $mydomain with 2 domains separate with a commas, but got error when restart postfix. Another problem is that I don't know where the error is for sending out mail from outlook expresss. Thanks in advance!

Would you mind reading the postfix doc first? This is a ways too easy task. You want to send out mail using outlook? Do you want to implement SMTP AUTH? Do you want to implement sender verification of SMTP AUTH?

For the relay domains part you need relay_domains = ... except you want those be deliverd at your box then you should take a look at the virtual stuff. If this doesn't help you out you should really take the time to read the docs. Postfix is pretty easy to setup ... postconf should be your friend also!