access (5)

Contents

NAME
SYNOPSIS
DESCRIPTION
CASE FOLDING
TABLE FORMAT
EMAIL ADDRESS PATTERNS
EMAIL ADDRESS EXTENSION
HOST NAME/ADDRESS PATTERNS
ACCEPT ACTIONS
REJECT ACTIONS
OTHER ACTIONS
ENHANCED STATUS CODES
REGULAR EXPRESSION TABLES
TCP-BASED TABLES
EXAMPLE
BUGS
SEE ALSO
README FILES
LICENSE
AUTHOR(S)

NAME

access - Postfix SMTP server access table

SYNOPSIS

postmap /etc/postfix/access

postmap -q "string" /etc/postfix/access

postmap -q - /etc/postfix/access <inputfile

DESCRIPTION

This document describes access control on remote SMTP client information: host names, network addresses, and envelope sender or recipient addresses; it is implemented by the Postfix SMTP server. See header_checks(5) or body_checks(5) for access control on the content of email messages.

Normally, the access(5) table is specified as a text file that serves as input to the postmap(1) command. The result, an indexed file in dbm or db format, is used for fast searching by the mail system. Execute the command "postmap /etc/postfix/access" to rebuild an indexed file after changing the corresponding text file.

When the table is provided via other means such as NIS, LDAP or SQL, the same lookups are done as for ordinary indexed files.

Alternatively, the table can be provided as a regular-expression map where patterns are given as regular expressions, or lookups can be directed to TCP-based server. In those cases, the lookups are done in a slightly different way as described below under "REGULAR EXPRESSION TABLES" or "TCP-BASED TABLES".

CASE FOLDING



The search string is folded to lowercase before database
lookup. As of Postfix 2.3, the search string is not case
folded with database types such as regexp: or pcre: whose
lookup fields can match both upper and lower case.


TABLE FORMAT






The input format for the postmap(1) command is as follows:



pattern action

When pattern matches a mail address, domain or host address,
perform the corresponding action.

blank lines and comments

Empty lines and whitespace-only lines are ignored, as
are lines whose first non-whitespace character is a `#'.

multi-line text

A logical line starts with non-whitespace text. A line that
starts with whitespace continues a logical line.




EMAIL ADDRESS PATTERNS






With lookups from indexed files such as DB or DBM, or from networked
tables such as NIS, LDAP or SQL, patterns are tried in the order as
listed below:



user@domain

Matches the specified mail address.

domain.tld

Matches domain.tld as the domain part of an email address.


The pattern domain.tld also matches subdomains, but only
when the string smtpd_access_maps is listed in the Postfix
parent_domain_matches_subdomains configuration setting.

.domain.tld

Matches subdomains of domain.tld, but only when the
string smtpd_access_maps is not listed in the Postfix
parent_domain_matches_subdomains configuration setting.

user@

Matches all mail addresses with the specified user part.





Note: lookup of the null sender address is not possible with
some types of lookup table. By default, Postfix uses <>
as the lookup key for such addresses. The value is specified with
the smtpd_null_access_lookup_key parameter in the Postfix
main.cf file.


EMAIL ADDRESS EXTENSION







When a mail address localpart contains the optional recipient delimiter
(e.g., user+foo@domain), the lookup order becomes:
user+foo@domain, user@domain, domain,
user+foo@, and user@.


HOST NAME/ADDRESS PATTERNS






With lookups from indexed files such as DB or DBM, or from networked
tables such as NIS, LDAP or SQL, the following lookup patterns are
examined in the order as listed:



domain.tld

Matches domain.tld.


The pattern domain.tld also matches subdomains, but only
when the string smtpd_access_maps is listed in the Postfix
parent_domain_matches_subdomains configuration setting.

.domain.tld

Matches subdomains of domain.tld, but only when the
string smtpd_access_maps is not listed in the Postfix
parent_domain_matches_subdomains configuration setting.

net.work.addr.ess


net.work.addr


net.work


net

Matches the specified IPv4 host address or subnetwork. An
IPv4 host address is a sequence of four decimal octets
separated by ".".


Subnetworks are matched by repeatedly truncating the last
".octet" from the remote IPv4 host address string until a
match is found in the access table, or until further
truncation is not possible.


NOTE 1: The access map lookup key must be in canonical form:
do not specify unnecessary null characters, and do not
enclose network address information with "[]" characters.


NOTE 2: use the cidr lookup table type to specify
network/netmask patterns. See cidr_table(5) for details.

net:work:addr:ess


net:work:addr


net:work


net

Matches the specified IPv6 host address or subnetwork. An
IPv6 host address is a sequence of three to eight hexadecimal
octet pairs separated by ":".


Subnetworks are matched by repeatedly truncating the last
":octetpair" from the remote IPv6 host address string until
a match is found in the access table, or until further
truncation is not possible.


NOTE 1: the truncation and comparison are done with the
string representation of the IPv6 host address. Thus, not
all the ":" subnetworks will be tried.


NOTE 2: The access map lookup key must be in canonical form:
do not specify unnecessary null characters, and do not
enclose network address information with "[]" characters.


NOTE 3: use the cidr lookup table type to specify
network/netmask patterns. See cidr_table(5) for details.


IPv6 support is available in Postfix 2.2 and later.




ACCEPT ACTIONS









OK

Accept the address etc. that matches the pattern.

all-numerical

An all-numerical result is treated as OK. This format is
generated by address-based relay authorization schemes
such as pop-before-smtp.





For other accept actions, see "OTHER ACTIONS" below.


REJECT ACTIONS






Postfix version 2.3 and later support enhanced status codes
as defined in RFC 3463.
When no code is specified at the beginning of the text
below, Postfix inserts a default enhanced status code of "5.7.1"
in the case of reject actions, and "4.7.1" in the case of
defer actions. See "ENHANCED STATUS CODES" below.



4NN text


5NN text

Reject the address etc. that matches the pattern, and respond with
the numerical three-digit code and text. 4NN means "try
again later", while 5NN means "do not try again".


The following responses have special meaning for the Postfix
SMTP server:





421 text (Postfix 2.3 and later)


521 text (Postfix 2.6 and later)

After responding with the numerical three-digit code and
text, disconnect immediately from the SMTP client.  This
frees up SMTP server resources so that they can be made
available to another SMTP client.


Note: The "521" response should be used only with botnets
and other malware where interoperability is of no concern.
The "send 521 and disconnect" behavior is NOT defined in
the SMTP standard.






REJECT optional text...

Reject the address etc. that matches the pattern. Reply with
"$access_map_reject_code optional text..." when the
optional text is
specified, otherwise reply with a generic error response message.

DEFER optional text...

Reject the address etc. that matches the pattern. Reply with
"$access_map_defer_code optional text..." when the
optional text is
specified, otherwise reply with a generic error response message.


This feature is available in Postfix 2.6 and later.

DEFER_IF_REJECT optional text...

Defer the request if some later restriction would result in a
REJECT action. Reply with "$access_map_defer_code 4.7.1
optional text..." when the
optional text is specified, otherwise reply with a generic error
response message.


Prior to Postfix 2.6, the SMTP reply code is 450.


This feature is available in Postfix 2.1 and later.

DEFER_IF_PERMIT optional text...

Defer the request if some later restriction would result in a
an explicit or implicit PERMIT action.
Reply with "$access_map_defer_code 4.7.1  optional
text..." when the
optional text is specified, otherwise reply with a generic error
response message.


Prior to Postfix 2.6, the SMTP reply code is 450.


This feature is available in Postfix 2.1 and later.





For other reject actions, see "OTHER ACTIONS" below.


OTHER ACTIONS









restriction...

Apply the named UCE restriction(s) (permit, reject,
reject_unauth_destination, and so on).

BCC user@domain

Send one copy of the message to the specified recipient.


If multiple BCC actions are specified within the same SMTP
MAIL transaction, only the last action will be used.


This feature is not part of the stable Postfix release.

DISCARD optional text...

Claim successful delivery and silently discard the message.
Log the optional text if specified, otherwise log a generic
message.


Note: this action currently affects all recipients of the message.
To discard only one recipient without discarding the entire message,
use the transport(5) table to direct mail to the discard(8) service.


This feature is available in Postfix 2.0 and later.

DUNNO

Pretend that the lookup key was not found. This
prevents Postfix from trying substrings of the lookup key
(such as a subdomain name, or a network address subnetwork).


This feature is available in Postfix 2.0 and later.

FILTER transport:destination

After the message is queued, send the entire message through
the specified external content filter. The transport
name specifies the first field of a mail delivery agent
definition in master.cf; the syntax of the next-hop
destination is described in the manual page of the
corresponding delivery agent.  More information about
external content filters is in the Postfix FILTER_README
file.


Note 1: do not use $number regular expression
substitutions for transport or destination
unless you know that the information has a trusted origin.


Note 2: this action overrides the main.cf content_filter
setting, and affects all recipients of the message. In the
case that multiple FILTER actions fire, only the last
one is executed.


Note 3: the purpose of the FILTER command is to override
message routing.  To override the recipient's transport
but not the next-hop destination, specify an empty
filter destination (Postfix 2.7 and later), or specify
a transport:destination that delivers through a
different Postfix instance (Postfix 2.6 and earlier). Other
options are using the recipient-dependent transport_maps
or the sender-dependent
sender_dependent_default_transport_maps
features.


This feature is available in Postfix 2.0 and later.

HOLD optional text...

Place the message on the hold queue, where it will
sit until someone either deletes it or releases it for
delivery.
Log the optional text if specified, otherwise log a generic
message.


Mail that is placed on hold can be examined with the
postcat(1) command, and can be destroyed or released with
the postsuper(1) command.


Note: use "postsuper -r" to release mail that was kept on
hold for a significant fraction of $maximal_queue_lifetime
or $bounce_queue_lifetime, or longer. Use "postsuper -H"
only for mail that will not expire within a few delivery attempts.


Note: this action currently affects all recipients of the message.


This feature is available in Postfix 2.0 and later.

PREPEND headername: headervalue

Prepend the specified message header to the message.
When more than one PREPEND action executes, the first
prepended header appears before the second etc. prepended
header.


Note: this action must execute before the message content
is received; it cannot execute in the context of
smtpd_end_of_data_restrictions.


This feature is available in Postfix 2.1 and later.

REDIRECT user@domain

After the message is queued, send the message to the specified
address instead of the intended recipient(s).


Note: this action overrides the FILTER action, and currently affects
all recipients of the message.


This feature is available in Postfix 2.1 and later.

WARN optional text...

Log a warning with the optional text, together with client information
and if available, with helo, sender, recipient and protocol information.


This feature is available in Postfix 2.1 and later.




ENHANCED STATUS CODES






Postfix version 2.3 and later support enhanced status codes
as defined in RFC 3463.
When an enhanced status code is specified in an access
table, it is subject to modification. The following
transformations are needed when the same access table is
used for client, helo, sender, or recipient access restrictions;
they happen regardless of whether Postfix replies to a MAIL
FROM, RCPT TO or other SMTP command.



•

When a sender address matches a REJECT action, the Postfix
SMTP server will transform a recipient DSN status (e.g.,
4.1.1-4.1.6) into the corresponding sender DSN status, and
vice versa.

•

When non-address information matches a REJECT action (such
as the HELO command argument or the client hostname/address),
the Postfix SMTP server will transform a sender or recipient
DSN status into a generic non-address DSN status (e.g.,
4.0.0).




REGULAR EXPRESSION TABLES






This section describes how the table lookups change when the table
is given in the form of regular expressions. For a description of
regular expression lookup table syntax, see regexp_table(5)
or pcre_table(5).


Each pattern is a regular expression that is applied to the entire
string being looked up. Depending on the application, that string
is an entire client hostname, an entire client IP address, or an
entire mail address. Thus, no parent domain or parent network search
is done, user@domain mail addresses are not broken up into
their user@ and domain constituent parts, nor is
user+foo broken up into user and foo.


Patterns are applied in the order as specified in the table, until a
pattern is found that matches the search string.


Actions are the same as with indexed file lookups, with
the additional feature that parenthesized substrings from the
pattern can be interpolated as $1, $2 and so on.


TCP-BASED TABLES






This section describes how the table lookups change when lookups
are directed to a TCP-based server. For a description of the TCP
client/server lookup protocol, see tcp_table(5).
This feature is not available up to and including Postfix version 2.4.


Each lookup operation uses the entire query string once.
Depending on the application, that string is an entire client
hostname, an entire client IP address, or an entire mail address.
Thus, no parent domain or parent network search is done,
user@domain mail addresses are not broken up into
their user@ and domain constituent parts, nor is
user+foo broken up into user and foo.


Actions are the same as with indexed file lookups.


EXAMPLE






The following example uses an indexed file, so that the
order of table entries does not matter. The example permits
access by the client at address 1.2.3.4 but rejects all
other clients in 1.2.3.0/24. Instead of hash lookup
tables, some systems use dbm.  Use the command
"postconf -m" to find out what lookup tables Postfix
supports on your system.



/etc/postfix/main.cf:
    smtpd_client_restrictions =
        check_client_access hash:/etc/postfix/access

/etc/postfix/access:
    1.2.3   REJECT
    1.2.3.4 OK






Execute the command "postmap /etc/postfix/access" after
editing the file.


BUGS




The table format does not understand quoting conventions.


SEE ALSO




postmap(1), Postfix lookup table manager
smtpd(8), SMTP server
postconf(5), configuration parameters
transport(5), transport:nexthop syntax



README FILES






Use "postconf readme_directory" or
"postconf html_directory" to locate this information.


SMTPD_ACCESS_README, built-in SMTP server access control
DATABASE_README, Postfix lookup table overview



LICENSE






The Secure Mailer license must be distributed with this software.


AUTHOR(S)




Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA