Introduction
============

Postfix version 2.0 introduces the concept of address classes.
This is a way of grouping recipient addresses by their delivery
method.  The idea comes from discussions with Victor Duchovni.

Benefits of address classes are:

- You no longer need to specify all the virtual(8) mailbox domains
  in the Postfix transport map. The virtual(8) delivery agent has
  become a first-class citizen just like local(8) or smtp(8).

- On mail gateway systems, separation of inbound mail relay traffic
  from outbound traffic. This eliminates a problem where inbound
  mail deliveries could become resource starved in the presence of
  a high volume of outbound mail.

- The SMTP server rejects unknown recipients in a more consistent
  manner than was possible with previous Postfix versions.

The list with "bad news" is at the end of this file :-)

What address classes does Postfix implement?
============================================

Initially the list of address classes is hard coded, but this is
meant to become extensible:

-------------------------------------------------------------------
Class	Description
-------------------------------------------------------------------
local	For UNIX accounts and for traditional /etc/aliases
	Domain names are listed in $mydestination (or match the IP
	    address listed with $inet_interfaces)
	Known recipients are listed in $local_recipient_maps (this
	    information is currently used by the Postfix SMTP server
	    only; if $local_recipient_maps is empty, the Postfix
	    SMTP server accepts all recipients)
	Default delivery agent: local

virtual For hosted domains that are aliased to mailboxes in other
alias	    domains
	Known recipients are listed in $virtual_alias_maps (default
	    is $virtual_maps for Postfix 1.1 compatibility)
	Domain names are listed in $virtual_alias_domains (default
	    is $virtual_alias_maps for Postfix 1.1 compatibility)

virtual	For hosted domains with their own mailboxes
mailbox	Known recipients are listed in $virtual_mailbox_maps (if
	    this parameter is empty, the Postfix SMTP server accepts
	    all recipients for domains listed in $virtual_mailbox_domains)
	Domain names are listed in $virtual_mailbox_domains (default
	    is $virtual_mailbox_maps for Postfix 1.1 compatibility)
	Default delivery agent: virtual

relay	For remote destinations that list your system as MX host
	Domain names are listed in $relay_domains
	Known recipients are listed in $relay_recipient_maps (if
	    this parameter is empty, the Postfix SMTP server accepts
	    all recipients for domains listed in $relay_domains)
	Default delivery agent: relay (clone of default smtp agent)

other	Restricted to mail from authorized clients
	Default delivery agent: smtp
	No domain table
	No recipient table
-------------------------------------------------------------------

Incompatibilities with Postfix 1.1
==================================

- virtual_maps is replaced by virtual_alias_maps (for address
  lookups) and virtual_alias_domains (for the names of what were
  formerly called "Postfix-style virtual domains").

  For backwards compatibility with Postfix version 1.1, the new
  virtual_alias_maps parameter defaults to $virtual_maps, and the
  new virtual_alias_domains parameter defaults to $virtual_alias_maps.

- virtual_mailbox_maps now has a companion parameter called
  virtual_mailbox_domains (for the names of domains served by the
  virtual delivery agent). virtual_mailbox_maps is now used for
  address lookups only.

  For backwards compatibility with Postfix version 1.1,, the new
  virtual_mailbox_domains parameter defaults to $virtual_mailbox_maps.

- Introduction of relay_recipient_maps, so that the Postfix SMTP
  server can block mail for relay recipients that don't exist. This
  list is empty by default.

- The local_recipient_maps feature is now turned on by default, so
  that the Postfix SMTP server rejects mail for unknown local
  recipients. This is enabled by default. See the LOCAL_RECIPIENT_README
  file hints and tips.

- Introduction of relay delivery transport in master.cf. This helps
  to avoid mail delivery scheduling problems on inbound mail relays,
  but may require that you update your "defer_transports" setting.