Postfix Installation From Source Code, Feb 8 2008
Send and receive mail via a virtual host interface, still without any change to an existing Sendmail installation.
Send and receive mail via a virtual host interface, still without any change to an existing Sendmail installation (section 8).
/etc/postfix/main.cf: myhostname = virtual.host.tld inet_interfaces = $myhostname
The first example is appropriate for a workstation, the second is appropriate for the mailserver for an entire domain. The third example should be used when running on a virtual host interface.
IMPORTANT: You must specify your proxy/NAT external addresses when your system is a backup MX host for other domains, otherwise mail delivery loops will happen when the primary MX host is down.
Example: host behind NAT box running a backup MX host.
10.7 - Optional: configure a smart host for remote delivery
If you're behind a firewall, you should set up a relayhost. If you can, specify the organizational domain name so that Postfix can use DNS lookups, and so that it can fall back to a secondary MX host when the primary MX host is down. Otherwise just specify a hard-coded hostname.
By default, the SMTP client will do DNS lookups even when you specify a relay host. If your machine has no access to a DNS server, turn off SMTP client DNS lookups like this:

SecurityPortal - Postfix - The Sendmail replacement part II, Feb 8 2008
host stench.seifried.org said: 554 <useraccount@stench.seifried.org>:
If incoming email does not match a virtual user, mapping it is sent to another address, in this example a local user called "bounce-local." It may then be blackholed to /dev/null, simply bounced (no such user), or sent to an admin email account - where it is deleted or forwarded to the correct person, if an obvious typo was made in the address, or whatever. You can also use a database backend instead of a hash or dbm file. This is definitely the way to go for large installations. See man virtual(5) for more information. Simply use the same machine as the outbound mail server (i.e., smart host) and it will rewrite the email addresses outgoing from @internal-mail.example.org to @example.org (or whatever you want).

Postfix Add-on Software, Feb 8 2008
policyd policy server in C which provides greylisting, sender (envelope, SASL or host/ip) based throttling (messages and/or volume per hour) and spamtraps by Cami Sardinha.
grinch utility by Daniel Mack. On request by Postfix, it finds out if a host is an open mail relay and caches the result.
system is a smart POP/IMAP proxy that connects users to the "right" POP/IMAP server.

Postfix Add-on Software, Feb 8 2008
policyd policy server in C which provides greylisting, sender (envelope, SASL or host/ip) based throttling (messages and/or volume per hour) and spamtraps by Cami Sardinha.
grinch utility by Daniel Mack. On request by Postfix, it finds out if a host is an open mail relay and caches the result.
system is a smart POP/IMAP proxy that connects users to the "right" POP/IMAP server.