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diff --git a/README_FILES/ADDRESS_CLASS_README b/README_FILES/ADDRESS_CLASS_README new file mode 100644 index 0000000..7605aa2 --- /dev/null +++ b/README_FILES/ADDRESS_CLASS_README @@ -0,0 +1,202 @@ +PPoossttffiixx AAddddrreessss CCllaasssseess + +------------------------------------------------------------------------------- + +IInnttrroodduuccttiioonn + +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. Although address classes introduced a few +incompatibilities they also made it possible to improve the handling of hosted +domains and of unknown recipients. + +This document provides information on the following topics: + + * What are address classes good for? + * What address classes does Postfix implement? + * Improvements compared to Postfix 1.1 + * Incompatibilities with Postfix 1.1 + +WWhhaatt aarree aaddddrreessss ccllaasssseess ggoooodd ffoorr?? + +Why should you care about address classes? This is how Postfix decides what +mail to accept, and how to deliver it. In other words, address classes are very +important for the operation of Postfix. + +An address class is defined by three items. + + * The list of domains that are a member of that address class: for example, + all local domains, or all relay domains. + + * The default delivery transport for that address class. For example, the + local, virtual or relay delivery transport (delivery transports are defined + in master.cf). This helps to keep Postfix configurations simple, by + avoiding the need for explicit routing information in transport maps. + + * The list of valid recipient addresses for that address class. The Postfix + SMTP server rejects invalid recipients with "User unknown in <name of + address class here> table". This helps to keep the Postfix queue free of + undeliverable MAILER-DAEMON messages. + +WWhhaatt aaddddrreessss ccllaasssseess ddooeess PPoossttffiixx iimmpplleemmeenntt?? + +Initially the list of address classes is hard coded, but this is meant to +become extensible. The summary below describes the main purpose of each class, +and what the relevant configuration parameters are. + +The local domain class. + + * Purpose: final delivery for traditional UNIX system accounts and + traditional Sendmail-style aliases. This is typically used for the + canonical domains of the machine (for example, $myhostname, $mydomain). For + a discussion of the difference between canonical domains, hosted domains + and other domains, see the VIRTUAL_README file. + + * Domain names are listed with the mydestination parameter. This domain class + also includes mail for user@[ipaddress] when the IP address is listed with + the inet_interfaces or proxy_interfaces parameters. + + * Valid recipient addresses are listed with the local_recipient_maps + parameter, as described in LOCAL_RECIPIENT_README. The Postfix SMTP server + rejects invalid recipients with "User unknown in local recipient table". If + the local_recipient_maps parameter value is empty, then the Postfix SMTP + server accepts any address in the local domain class. + + * The mail delivery transport is specified with the local_transport + parameter. The default value is llooccaall::$$mmyyhhoossttnnaammee for delivery with the + local(8) delivery agent. + +The virtual alias domain class. + + * Purpose: hosted domains where each recipient address is aliased to an + address in a different domain, for example, a local UNIX system account or + a remote address. A virtual alias example is given in the VIRTUAL_README + file. + + * Domain names are listed in virtual_alias_domains. The default value is + $virtual_alias_maps for Postfix 1.1 compatibility. + + * Valid recipient addresses are listed with the virtual_alias_maps parameter. + The Postfix SMTP server rejects invalid recipients with "User unknown in + virtual alias table". The default value is $virtual_maps for Postfix 1.1 + compatibility. + + * There is no mail delivery transport parameter. Every address must be + aliased to an address in some other domain. + +The virtual mailbox domain class. + + * Purpose: final delivery for hosted domains where each recipient address can + have its own mailbox, and where users do not need to have a UNIX system + account. A virtual mailbox example is given in the VIRTUAL_README file. + + * Domain names are listed with the virtual_mailbox_domains parameter. The + default value is $virtual_mailbox_maps for Postfix 1.1 compatibility. + + * Valid recipient addresses are listed with the virtual_mailbox_maps + parameter. The Postfix SMTP server rejects invalid recipients with "User + unknown in virtual mailbox table". If this parameter value is empty, the + Postfix SMTP server accepts all recipients for domains listed in + $virtual_mailbox_domains. + + * The mail delivery transport is specified with the virtual_transport + parameter. The default value is vviirrttuuaall for delivery with the virtual(8) + delivery agent. + +The relay domain class. + + * Purpose: mail forwarding to remote destinations that list your system as + primary or backup MX host. For a discussion of the basic configuration + details, see the BASIC_CONFIGURATION_README document. For a discussion of + the difference between canonical domains, hosted domains and other domains, + see the VIRTUAL_README file. + + * Domain names are listed with the relay_domains parameter. + + * Valid recipient addresses are listed with the relay_recipient_maps + parameter. The Postfix SMTP server rejects invalid recipients with "User + unknown in relay recipient table". If this parameter value is empty, the + Postfix SMTP server accepts all recipients for domains listed with the + relay_domains parameter. + + * The mail delivery transport is specified with the relay_transport + parameter. The default value is rreellaayy which is a clone of the smtp(8) + delivery agent. + +The default domain class. + + * Purpose: mail forwarding to the Internet on behalf of authorized clients. + For a discussion of the basic configuration details, see the + BASIC_CONFIGURATION_README file. For a discussion of the difference between + canonical domains, hosted domains and other domains, see the VIRTUAL_README + file. + + * This class has no destination domain table. + + * This class has no valid recipient address table. + + * The mail delivery transport is specified with the default_transport + parameter. The default value is ssmmttpp for delivery with the smtp(8) delivery + agent. + +IImmpprroovveemmeennttss ccoommppaarreedd ttoo PPoossttffiixx 11..11 + +Postfix 2.0 address classes made the following improvements possible over +earlier Postfix versions: + + * 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, address classes provide separation of inbound mail + relay traffic ($relay_transport) from outbound traffic + ($default_transport). 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 Postfix version 1. This is needed to keep undeliverable + mail (and bounced undeliverable mail) out of the mail queue. This is + controlled by the smtpd_reject_unlisted_recipient configuration parameter. + + * As of Postfix version 2.1, the SMTP server can also reject unknown sender + addresses (i.e. addresses that it would reject as an unknown recipient + addresses). Sender "egress filtering" can help to slow down an email worm + explosion. This is controlled by the smtpd_reject_unlisted_sender + configuration parameter. + +IInnccoommppaattiibbiilliittiieess wwiitthh PPoossttffiixx 11..11 + +Postfix 2.0 address classes introduce a few incompatible changes in documented +behavior. In order to ease the transitions, new parameters have default values +that are backwards compatible. + + * The virtual_maps parameter is replaced by virtual_alias_maps (for address + lookups) and by 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. + + * The virtual_mailbox_maps parameter now has a companion parameter called + virtual_mailbox_domains (for the names of domains served by the virtual + delivery agent). The virtual_mailbox_maps parameter 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 the relay_recipient_maps parameter. The Postfix SMTP server + can use this to block mail for relay recipients that don't exist. This list + is empty by default, which means accept any recipient. + + * The local_recipient_maps feature is now turned on by default. The Postfix + SMTP server uses this to reject mail for unknown local recipients. See the + LOCAL_RECIPIENT_README file hints and tips. + + * Introduction of the relay delivery transport in master.cf. This helps to + avoid mail delivery scheduling problems on inbound mail relays when there + is a lot of outbound mail, but may require that you update your + "defer_transports" setting. + |