What domain name to use in outbound mail
The myorigin parameter specifies the domain that appears in mail that is posted on this machine. The default is to use the local machine name, $myhostname, which defaults to the name of the machine. Unless you are running a really small site, you probably want to change that into $mydomain, which defaults to the parent domain of the machine name.
For the sake of consistency between sender and recipient addresses, myorigin also specifies the domain name that is appended to an unqualified recipient address.
Examples (specify only one of the following):
/etc/postfix/main.cf:
myorigin = $myhostname (default: send mail as “user@$myhostname”)
myorigin = $mydomain (probably desirable: “user@$mydomain”)
What domains to receive mail for
The mydestination parameter specifies what domains this machine will deliver locally, instead of forwarding to another machine. The default is to receive mail for the machine itself. See the VIRTUAL_README file for how to configure Postfix for hosted domains.
You can specify zero or more domain names, “/file/name” patterns and/or “type:table” lookup tables (such as hash:, btree:, nis:, ldap:, or mysql:), separated by whitespace and/or commas. A “/file/name” pattern is replaced by its contents; “type:table” requests that a table lookup is done and merely tests for existence: the lookup result is ignored.
IMPORTANT: If your machine is a mail server for its entire domain, you must list $mydomain as well.
Example 1: default setting.
/etc/postfix/main.cf:
mydestination = $myhostname localhost.$mydomain localhost
Example 2: domain-wide mail server.
/etc/postfix/main.cf:
mydestination = $myhostname localhost.$mydomain localhost $mydomain
Example 3: host with multiple DNS A records.
/etc/postfix/main.cf:
mydestination = $myhostname localhost.$mydomain localhost
www.$mydomain ftp.$mydomain
Caution: in order to avoid mail delivery loops, you must list all hostnames of the machine, including $myhostname, and localhost.$mydomain.