Updated: 2022/Sep/29
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ACCESS(5) File Formats Manual ACCESS(5)
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 a 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 a remote IPv4 host address or network address range.
Specify one to four decimal octets separated by ".". Do not
specify "[]" , "/", leading zeros, or hexadecimal forms.
Network ranges are matched by repeatedly truncating the last
".octet" from a remote IPv4 host address string, until a match
is found in the access table, or until further truncation is not
possible.
NOTE: 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 a remote IPv6 host address or network address range.
Specify three to eight hexadecimal octet pairs separated by ":",
using the compressed form "::" for a sequence of zero-valued
octet pairs. Do not specify "[]", "/", leading zeros, or
non-compressed forms.
A network range is matched by repeatedly truncating the last
":octetpair" from the compressed-form remote IPv6 host address
string, until a match is found in the access table, or until
further truncation is not possible.
NOTE: 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 "$access_map_defer_code 4.7.1 optional
text..." when the optional text is specified, otherwise reply
with a generic error response message.
Prior to Postfix 2.6, the SMTP reply code is 450.
This feature is available in Postfix 2.1 and later.
DEFER_IF_PERMIT optional text...
Defer the request if some later restriction would result in an
explicit or implicit PERMIT action. Reply with
"$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, with Postfix 3.0 only the last action will be used.
This feature is available in Postfix 3.0 and later.
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). When multiple
REDIRECT actions fire, only the last one takes effect.
Note: this action overrides the FILTER action, and currently
overrides all recipients of the message.
This feature is available in Postfix 2.1 and later.
INFO optional text...
Log an informational record with the optional text, together
with client information and if available, with helo, sender,
recipient and protocol information.
This feature is available in Postfix 3.0 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
Wietse Venema
Google, Inc.
111 8th Avenue
New York, NY 10011, USA
ACCESS(5)