The Postfix queue manager sorts mail according to its destination
and gives it to Postfix delivery agents such as
local(8),
smtp(8),
or
lmtp(8). Just like the
cleanup(8) server, the Postfix queue
manager delegates the more complex address manipulations to the
trivial-rewrite(8) server.
Address manipulations at this stage are:
Each Postfix delivery agent tries to deliver the mail to its
destination, while encapsulating the sender, recipients, and message
content according to the rules of the SMTP, LMTP, etc. protocol.
When mail cannot be delivered, it is either returned to the sender
or moved to the
deferred queue and tried again later.
Address manipulations when mail is delivered
via the
smtp(8) delivery agent:
Address manipulations when mail is delivered
via the
local(8) delivery agent:
The remainder of this document presents each address manipulation
step in more detail, with specific examples or with pointers to
documentation with examples.
The Postfix
qmgr(8) queue manager selects new mail from the
incoming queue or old mail from the
deferred queue, and asks the
trivial-rewrite(8) address rewriting and resolving daemon where it
should be delivered.
As of version 2.0, Postfix distinguishes four major address
classes. Each class has its own list of domain names, and each
class has its own default delivery method, as shown in the table
below. See the
ADDRESS_CLASS_README document for the fine details.
Postfix versions before 2.0 only distinguish between local delivery
and everything else.
Once the
trivial-rewrite(8) daemon has determined a default
delivery method it searches the optional
transport(5) table for
information that overrides the message destination and/or delivery
method. Typical use of the
transport(5) table is to send mail to
a system
that is not connected to the Internet, or to use a special SMTP
client configuration for destinations that have special requirements.
See, for example, the
STANDARD_CONFIGURATION_README and
UUCP_README
documents, and the examples in the
transport(5) manual page.
Transport table lookups are disabled by default. To enable,
edit the
transport_maps parameter in the
main.cf file and specify
one or more lookup tables, separated by whitespace or commas.
Example:
/etc/postfix/
main.cf:
transport_maps = hash:/etc/postfix/transport
Next, the
trivial-rewrite(8) address rewriting and resolving
daemon runs each recipient through the
relocated(5) database. This
table provides information on how to reach users that no longer
have an account, or what to do with mail for entire domains that
no longer exist. When mail is sent to an address that is listed
in this table, the message is returned to the sender with an
informative message.
The
relocated(5) database is searched after
transport(5)
table lookups, in anticipation of
transport(5) tables that
can replace one recipient address by a different one.
Lookups of relocated users are disabled by default. To enable,
edit the
relocated_maps parameter in the
main.cf file and specify
one or more lookup tables, separated by whitespace or commas.
Example:
/etc/postfix/
main.cf:
relocated_maps = hash:/etc/postfix/relocated
/etc/postfix/relocated:
[email protected] [email protected]
As of Postfix version 2, mail for a relocated user will be
rejected by the SMTP server with the reason "user has moved to
[email protected]". Older Postfix versions will receive the
mail first, and then return it to the sender as undeliverable, with
the same reason.
Some hosts have no valid Internet domain name, and instead use
a name such as localdomain.local. This can be a problem when
you want to send mail over the Internet, because many mail servers
reject mail addresses with invalid domain names.
With the
smtp_generic_maps parameter you can specify
generic(5)
lookup tables that replace local mail addresses by valid Internet
addresses when mail leaves the machine via SMTP. The
generic(5)
mapping replaces envelope and header addresses, and is non-recursive.
It does not happen when you send mail between addresses on the
local machine.
This feature is available in Postfix version 2.2 and later.
Example:
/etc/postfix/
main.cf:
smtp_generic_maps = hash:/etc/postfix/generic
/etc/postfix/generic:
[email protected] [email protected]
[email protected] [email protected]
@localdomain.local [email protected]
When mail is sent to a remote host via SMTP, this replaces
[email protected] by his ISP mail address, replaces
[email protected] by her ISP mail address, and replaces
other local addresses by his ISP account, with an address extension
of +local (this example assumes that the ISP supports "+"
style address extensions).
When mail is to be delivered locally, the
local(8) delivery
agent runs each local recipient name through the
aliases(5) database.
The mapping does not affect addresses in message headers. Local
aliases are typically used to implement distribution lists, or to
direct mail for standard aliases such as postmaster to real people.
The table can also be used to map "Firstname.Lastname" addresses
to login names.
Alias lookups are enabled by default. The default configuration
depends on the operating system environment, but it is typically
one of the following:
/etc/postfix/
main.cf:
alias_maps = hash:/etc/aliases
alias_maps = dbm:/etc/aliases, nis:mail.aliases
The pathname of the alias database file is controlled with the
alias_database configuration parameter. The value is system dependent.
Usually it is one of the following:
/etc/postfix/
main.cf:
alias_database = hash:/etc/aliases (4.4BSD, LINUX)
alias_database = dbm:/etc/aliases (4.3BSD, SYSV<4)
alias_database = dbm:/etc/mail/aliases (SYSV4)
An
aliases(5) file can specify that mail should be delivered
to a local file, or to a command that receives the message in the
standard input stream. For security reasons, deliveries to command
and file destinations are performed with the rights of the alias
database owner. A default userid,
default_privs, is used for
deliveries to commands or files in "root"-owned aliases.
With delivery via the
local(8) deliver agent, users can control
their own mail delivery by specifying destinations in a file called
.forward in their home directories. The syntax of these files is
the same as with the local
aliases(5) file, except that the left-hand
side of the alias (lookup key and colon) are not present.
When the
local(8) delivery agent finds that a message recipient
does not exist, the message is normally returned to the sender ("user
unknown"). Sometimes it is desirable to forward mail for non-existing
recipients to another machine. For this purpose you can specify
an alternative destination with the
luser_relay configuration
parameter.
Alternatively, mail for non-existent recipients can be delegated
to an entirely different message transport, as specified with the
fallback_transport configuration parameter. For details, see the
local(8) delivery agent documentation.
Note: if you use the
luser_relay feature in order to receive
mail for non-UNIX accounts, then you must specify:
/etc/postfix/
main.cf:
local_recipient_maps =
(i.e. empty) in the
main.cf file, otherwise the Postfix SMTP
server will reject mail for non-UNIX accounts with "User unknown
in local recipient table". See the
LOCAL_RECIPIENT_README file
for more information on this.
luser_relay can specify one address. It is subjected to "$name"
expansions. Examples:
- [email protected]
-
The bare username, without address extension, is prepended
to "@other.host". For example, mail for "username+foo" is sent to
"[email protected]".
- [email protected]
-
The entire original recipient localpart, including address
extension, is prepended to "@other.host". For example, mail for
"username+foo" is sent to "[email protected]".
- sysadmin+$user
-
The bare username, without address extension, is appended
to "sysadmin". For example, mail for "username+foo" is sent to
"sysadmin+username".
- sysadmin+$local
-
The entire original recipient localpart, including address
extension, is appended to "sysadmin". For example, mail for
"username+foo" is sent to "sysadmin+username+foo".
