postqueue -f

vi /etc/postfix/main.cf
relayhost = smarthost.server.name

smtpd_recipient_restrictions =
reject_invalid_hostname,
reject_non_fqdn_sender,
reject_non_fqdn_recipient,
reject_unknown_sender_domain,
reject_unknown_recipient_domain,
reject_unauth_pipelining,
permit_mynetworks,
reject_unauth_destination,
reject_rbl_client bl.spamcop.net
permit

Postfix by default on CentOS and Red Hat Enterprise Linux is configured to only receive mail on the local network interface.

vi /etc/postfix/main.cf
inet_interfaces = localhost LOCAL_IP

vi /etc/postfix/main.cf
virtual_alias_domains = linux4you.tk
virtual_alias_maps = hash:/etc/postfix/virtual

vi /etc/postfix/virtual
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postmap /etc/postfix/virtual
service postfix reload