ldap_table (5)

Contents

NAME
SYNOPSIS
DESCRIPTION
BACKWARDS COMPATIBILITY
LIST MEMBERSHIP
GENERAL LDAP PARAMETERS
LDAP SASL PARAMETERS
LDAP SSL AND STARTTLS PARAMETERS
EXAMPLE
SEE ALSO
README FILES
LICENSE
AUTHOR(S)

NAME

ldap_table - Postfix LDAP client configuration

SYNOPSIS

postmap -q "string" ldap:/etc/postfix/filename

postmap -q - ldap:/etc/postfix/filename <inputfile

DESCRIPTION

The Postfix mail system uses optional tables for address rewriting or mail routing. These tables are usually in dbm or db format.

Alternatively, lookup tables can be specified as LDAP databases.

In order to use LDAP lookups, define an LDAP source as a lookup table in main.cf, for example: 

    alias_maps = ldap:/etc/postfix/ldap-aliases.cf

The file /etc/postfix/ldap-aliases.cf has the same format as the Postfix main.cf file, and can specify the parameters described below. An example is given at the end of this manual.

This configuration method is available with Postfix version 2.1 and later. See the section "BACKWARDS COMPATIBILITY" below for older Postfix versions.

For details about LDAP SSL and STARTTLS, see the section on SSL and STARTTLS below.

BACKWARDS COMPATIBILITY



For backwards compatibility with Postfix version 2.0 and earlier,
LDAP parameters can also be defined in main.cf.  Specify
as LDAP source a name that doesn't begin with a slash or
a dot.  The LDAP parameters will then be accessible as the
name you've given the source in its definition, an underscore,
and the name of the parameter.  For example, if the map is
specified as "ldap:ldapsource", the "server_host"
parameter below would be defined in main.cf as
"ldapsource_server_host".


Note: with this form, the passwords for the LDAP sources are
written in main.cf, which is normally world-readable.  Support
for this form will be removed in a future Postfix version.


For backwards compatibility with the pre
2.2 LDAP clients, result_filter can for now be used instead
of result_format, when the latter parameter is not also set.
The new name better reflects the function of the parameter. This
compatibility interface may be removed in a future release.


LIST MEMBERSHIP






When using LDAP to store lists such as $mynetworks,
$mydestination, $relay_domains, $local_recipient_maps,
etc., it is important to understand that the table must
store each list member as a separate key. The table lookup
verifies the *existence* of the key. See "Postfix lists
versus tables" in the DATABASE_README document for a
discussion.


Do NOT create tables that return the full list of domains
in $mydestination or $relay_domains etc., or IP addresses
in $mynetworks.


DO create tables with each matching item as a key and with
an arbitrary value. With LDAP databases it is not uncommon to
return the key itself.


For example, NEVER do this in a map defining $mydestination:



    query_filter = domain=*
    result_attribute = domain





Do this instead:



    query_filter = domain=%s
    result_attribute = domain





GENERAL LDAP PARAMETERS






In the text below, default values are given in parentheses.
Note: don't use quotes in these variables; at least, not until the
Postfix configuration routines understand how to deal with quoted
strings.



server_host (default: localhost)

The name of the host running the LDAP server, e.g.



    server_host = ldap.example.com





Depending on the LDAP client library you're using, it should
be possible to specify multiple servers here, with the library
trying them in order should the first one fail. It should also
be possible to give each server in the list a different port
(overriding server_port below), by naming them like



    server_host = ldap.example.com:1444





With OpenLDAP, a (list of) LDAP URLs can be used to specify both
the hostname(s) and the port(s):



    server_host = ldap://ldap.example.com:1444
                ldap://ldap2.example.com:1444





All LDAP URLs accepted by the OpenLDAP library are supported,
including connections over UNIX domain sockets, and LDAP SSL
(the last one provided that OpenLDAP was compiled with support
for SSL):



    server_host = ldapi://%2Fsome%2Fpath
                ldaps://ldap.example.com:636




server_port (default: 389)

The port the LDAP server listens on, e.g.



    server_port = 778




timeout (default: 10 seconds)

The number of seconds a search can take before timing out, e.g.




    timeout = 5


search_base (No default; you must configure this)

The RFC2253 base DN at which to conduct the search, e.g.



    search_base = dc=your, dc=com





With Postfix 2.2 and later this parameter supports the
following '%' expansions:





%%

This is replaced by a literal '%' character.

%s

This is replaced by the input key.
RFC 2253 quoting is used to make sure that the input key
does not add unexpected metacharacters.

%u

When the input key is an address of the form user@domain, %u
is replaced by the (RFC 2253) quoted local part of the address.
Otherwise, %u is replaced by the entire search string.
If the localpart is empty, the search is suppressed and returns
no results.

%d

When the input key is an address of the form user@domain, %d
is replaced by the (RFC 2253) quoted domain part of the address.
Otherwise, the search is suppressed and returns no results.

%[SUD]

For the search_base parameter, the upper-case equivalents
of the above expansions behave identically to their lower-case
counter-parts. With the result_format parameter (previously
called result_filter see the COMPATIBILITY section and below),
they expand to the corresponding components of input key rather
than the result value.

%[1-9]

The patterns %1, %2, ... %9 are replaced by the corresponding
most significant component of the input key's domain. If the
input key is user@mail.example.com, then %1 is com,
%2 is example and %3 is mail. If the input key is
unqualified or does not have enough domain components to satisfy
all the specified patterns, the search is suppressed and returns
no results.






query_filter (default: mailacceptinggeneralid=%s)

The RFC2254 filter used to search the directory, where %s
is a substitute for the address Postfix is trying to resolve,
e.g.



    query_filter = (&(mail=%s)(paid_up=true))





This parameter supports the following '%' expansions:





%%

This is replaced by a literal '%' character. (Postfix 2.2 and later).

%s

This is replaced by the input key.
RFC 2254 quoting is used to make sure that the input key
does not add unexpected metacharacters.

%u

When the input key is an address of the form user@domain, %u
is replaced by the (RFC 2254) quoted local part of the address.
Otherwise, %u is replaced by the entire search string.
If the localpart is empty, the search is suppressed and returns
no results.

%d

When the input key is an address of the form user@domain, %d
is replaced by the (RFC 2254) quoted domain part of the address.
Otherwise, the search is suppressed and returns no results.

%[SUD]

The upper-case equivalents of the above expansions behave in the
query_filter parameter identically to their lower-case
counter-parts. With the result_format parameter (previously
called result_filter see the COMPATIBILITY section and below),
they expand to the corresponding components of input key rather
than the result value.


The above %S, %U and %D expansions are available with Postfix 2.2
and later.

%[1-9]

The patterns %1, %2, ... %9 are replaced by the corresponding
most significant component of the input key's domain. If the
input key is user@mail.example.com, then %1 is com,
%2 is example and %3 is mail. If the input key is
unqualified or does not have enough domain components to satisfy
all the specified patterns, the search is suppressed and returns
no results.


The above %1, ..., %9 expansions are available with Postfix 2.2
and later.







The "domain" parameter described below limits the input
keys to addresses in matching domains. When the "domain"
parameter is non-empty, LDAP queries for unqualified
addresses or addresses in non-matching domains are suppressed
and return no results.


NOTE: DO NOT put quotes around the query_filter parameter.

result_format (default: %s)

Called result_filter in Postfix releases prior to 2.2.
Format template applied to result attributes. Most commonly used
to append (or prepend) text to the result. This parameter supports
the following '%' expansions:





%%

This is replaced by a literal '%' character. (Postfix 2.2 and later).

%s

This is replaced by the value of the result attribute. When
result is empty it is skipped.

%u

When the result attribute value is an address of the form
user@domain, %u is replaced by the local part of the
address. When the result has an empty localpart it is skipped.

%d

When a result attribute value is an address of the form
user@domain, %d is replaced by the domain part of
the attribute value. When the result is unqualified it
is skipped.

%[SUD1-9]

The upper-case and decimal digit expansions interpolate
the parts of the input key rather than the result. Their
behavior is identical to that described with query_filter,
and in fact because the input key is known in advance, lookups
whose key does not contain all the information specified in
the result template are suppressed and return no results.


The above %S, %U, %D and %1, ..., %9 expansions are available with
Postfix 2.2 and later.







For example, using "result_format = smtp:[%s]" allows one
to use a mailHost attribute as the basis of a transport(5)
table. After applying the result format, multiple values
are concatenated as comma separated strings. The expansion_limit
and size_limit parameters explained below allow one to
restrict the number of values in the result, which is
especially useful for maps that should return a single
value.


The default value %s specifies that each
attribute value should be used as is.


This parameter was called result_filter in Postfix
releases prior to 2.2. If no "result_format" is specified,
the value of "result_filter" will be used instead before
resorting to the default value. This provides compatibility
with old configuration files.


NOTE: DO NOT put quotes around the result format!

domain (default: no domain list)

This is a list of domain names, paths to files, or
dictionaries. When specified, only fully qualified search
keys with a *non-empty* localpart and a matching domain
are eligible for lookup: 'user' lookups, bare domain lookups
and "@domain" lookups are not performed. This can significantly
reduce the query load on the LDAP server.



    domain = postfix.org, hash:/etc/postfix/searchdomains





It is best not to use LDAP to store the domains eligible
for LDAP lookups.


NOTE: DO NOT define this parameter for local(8) aliases.


This feature is available in Postfix 1.0 and later.

result_attribute (default: maildrop)

The attribute(s) Postfix will read from any directory
entries returned by the lookup, to be resolved to an email
address.



    result_attribute = mailbox, maildrop





Don't rely on the default value ("maildrop"). Set the
result_attribute explicitly in all ldap table configuration
files. This is particularly relevant when no result_attribute
is applicable, e.g. cases in which leaf_result_attribute and/or
terminal_result_attribute are used instead. The default value
is harmless if "maildrop" is also listed as a leaf or terminal
result attribute, but it is best to not leave this to chance.

special_result_attribute (default: empty)

The attribute(s) of directory entries that can contain DNs
or RFC 2255 LDAP URLs. If found, a recursive search
is performed to retrieve the entry referenced by the DN, or
the entries matched by the URL query.



    special_result_attribute = memberdn





DN recursion retrieves the same result_attributes as the
main query, including the special attributes for further
recursion.


URL processing retrieves only those attributes that are included
in both the URL definition and as result attributes (ordinary,
special, leaf or terminal) in the Postfix table definition.
If the URL lists any of the table's special result attributes,
these are retrieved and used recursively. A URL that does not
specify any attribute selection, is equivalent (RFC 2255) to a
URL that selects all attributes, in which case the selected
attributes will be the full set of result attributes in the
Postfix table.


If an LDAP URL attribute-descriptor or the corresponding Postfix
LDAP table result attribute (but not both) uses RFC 2255 sub-type
options ("attr;option"), the attribute requested from the LDAP server
will include the sub-type option. In all other cases, the URL
attribute and the table attribute must match exactly. Attributes
with options in both the URL and the Postfix table are requested
only when the options are identical. LDAP attribute-descriptor
options are very rarely used, most LDAP users will not
need to concern themselves with this level of nuanced detail.

terminal_result_attribute (default: empty)

When one or more terminal result attributes are found in an LDAP
entry, all other result attributes are ignored and only the terminal
result attributes are returned. This is useful for delegating expansion
of group members to a particular host, by using an optional "maildrop"
attribute on selected groups to route the group to a specific host,
where the group is expanded, possibly via mailing-list manager or
other special processing.



    result_attribute =
    terminal_result_attribute = maildrop





When using terminal and/or leaf result attributes, the
result_attribute is best set to an empty value when it is not
used, or else explicitly set to the desired value, even if it is
the default value "maildrop".


This feature is available with Postfix 2.4 or later.

leaf_result_attribute (default: empty)

When one or more special result attributes are found in a non-terminal
(see above) LDAP entry, leaf result attributes are excluded from the
expansion of that entry. This is useful when expanding groups and the
desired mail address attribute(s) of the member objects obtained via
DN or URI recursion are also present in the group object. To only
return the attribute values from the leaf objects and not the
containing group, add the attribute to the leaf_result_attribute list,
and not the result_attribute list, which is always expanded. Note,
the default value of "result_attribute" is not empty, you may want to
set it explicitly empty when using "leaf_result_attribute" to expand
the group to a list of member DN addresses. If groups have both
member DN references AND attributes that hold multiple string valued
rfc822 addresses, then the string attributes go in "result_attribute".
The attributes that represent the email addresses of objects
referenced via a DN (or LDAP URI) go in "leaf_result_attribute".



    result_attribute = memberaddr
    special_result_attribute = memberdn
    terminal_result_attribute = maildrop
    leaf_result_attribute = mail





When using terminal and/or leaf result attributes, the
result_attribute is best set to an empty value when it is not
used, or else explicitly set to the desired value, even if it is
the default value "maildrop".


This feature is available with Postfix 2.4 or later.

scope (default: sub)

The LDAP search scope: sub, base, or one.
These translate into LDAP_SCOPE_SUBTREE, LDAP_SCOPE_BASE,
and LDAP_SCOPE_ONELEVEL.

bind (default: yes)

Whether or how to bind to the LDAP server. Newer LDAP
implementations don't require clients to bind, which saves
time. Example:



    # Don't bind
    bind = no
    # Use SIMPLE bind
    bind = yes
    # Use SASL bind
    bind = sasl





Postfix versions prior to 2.8 only support "bind = no" which
means don't bind, and "bind = yes" which means do a SIMPLE bind.
Postfix 2.8 and later also supports "bind = SASL" when compiled
with LDAP SASL support as described in LDAP_README, it also adds
the synonyms "bind = none" and "bind = simple" for "bind = no"
and "bind = yes" respectively. See the SASL section below for
additional parameters available with "bind = sasl".


If you do need to bind, you might consider configuring
Postfix to connect to the local machine on a port that's
an SSL tunnel to your LDAP server. If your LDAP server
doesn't natively support SSL, put a tunnel (wrapper, proxy,
whatever you want to call it) on that system too. This
should prevent the password from traversing the network in
the clear.

bind_dn (default: empty)

If you do have to bind, do it with this distinguished name. Example:



    bind_dn = uid=postfix, dc=your, dc=com



With "bind = sasl" (see above) the DN may be optional for some SASL
mechanisms, don't specify a DN if not needed.

bind_pw (default: empty)

The password for the distinguished name above. If you have
to use this, you probably want to make the map configuration
file readable only by the Postfix user. When using the
obsolete ldap:ldapsource syntax, with map parameters in
main.cf, it is not possible to securely store the bind
password. This is because main.cf needs to be world readable
to allow local accounts to submit mail via the sendmail
command. Example:



    bind_pw = postfixpw



With "bind = sasl" (see above) the password may be optional
for some SASL mechanisms, don't specify a password if not needed.

cache (IGNORED with a warning)


cache_expiry (IGNORED with a warning)


cache_size (IGNORED with a warning)

The above parameters are NO LONGER SUPPORTED by Postfix.
Cache support has been dropped from OpenLDAP as of release
2.1.13.

recursion_limit (default: 1000)

A limit on the nesting depth of DN and URL special result
attribute evaluation. The limit must be a non-zero positive
number.

expansion_limit (default: 0)

A limit on the total number of result elements returned
(as a comma separated list) by a lookup against the map.
A setting of zero disables the limit. Lookups fail with a
temporary error if the limit is exceeded.  Setting the
limit to 1 ensures that lookups do not return multiple
values.

size_limit (default: $expansion_limit)

A limit on the number of LDAP entries returned by any single
LDAP search performed as part of the lookup. A setting of
0 disables the limit.  Expansion of DN and URL references
involves nested LDAP queries, each of which is separately
subjected to this limit.


Note: even a single LDAP entry can generate multiple lookup
results, via multiple result attributes and/or multi-valued
result attributes. This limit caps the per search resource
utilization on the LDAP server, not the final multiplicity
of the lookup result. It is analogous to the "-z" option
of "ldapsearch".

dereference (default: 0)

When to dereference LDAP aliases. (Note that this has
nothing do with Postfix aliases.) The permitted values are
those legal for the OpenLDAP/UM LDAP implementations:





0

never

1

when searching

2

when locating the base object for the search

3

always







See ldap.h or the ldap_open(3) or ldapsearch(1) man pages
for more information. And if you're using an LDAP package
that has other possible values, please bring it to the
attention of the postfix-users@postfix.org mailing list.

chase_referrals (default: 0)

Sets (or clears) LDAP_OPT_REFERRALS (requires LDAP version
3 support).

version (default: 2)

Specifies the LDAP protocol version to use.

debuglevel (default: 0)

What level to set for debugging in the OpenLDAP libraries.




LDAP SASL PARAMETERS






If you're using the OpenLDAP libraries compiled with SASL
support, Postfix 2.8 and later built with LDAP SASL support
as described in LDAP_README can authenticate to LDAP servers
via SASL.


This enables authentication to the LDAP server via mechanisms
other than a simple password. The added flexibility has a cost:
it is no longer practical to set an explicit timeout on the duration
of an LDAP bind operation. Under adverse conditions, whether a SASL
bind times out, or if it does, the duration of the timeout is
determined by the LDAP and SASL libraries.


It is best to use tables that use SASL binds via proxymap(8), this
way the requesting process can time-out the proxymap request. This
also lets you tailer the process environment by overriding the
proxymap(8) import_environment setting in master.cf(5). Special
environment settings may be needed to configure GSSAPI credential
caches or other SASL mechanism specific options. The GSSAPI
credentials used for LDAP lookups may need to be different than
say those used for the Postfix SMTP client to authenticate to remote
servers.


Using SASL mechanisms requires LDAP protocol version 3, the default
protocol version is 2 for backwards compatibility. You must set
"version = 3" in addition to "bind = sasl".


The following parameters are relevant to using LDAP with SASL



sasl_mechs (default: empty)

Space separated list of SASL mechanism(s) to try.

sasl_realm (default: empty)

SASL Realm to use, if applicable.

sasl_authz_id (default: empty)

The SASL authorization identity to assert, if applicable.

sasl_minssf (default: 0)

The minimum required sasl security factor required to establish a
connection.




LDAP SSL AND STARTTLS PARAMETERS






If you're using the OpenLDAP libraries compiled with SSL
support, Postfix can connect to LDAP SSL servers and can
issue the STARTTLS command.


LDAP SSL service can be requested by using a LDAP SSL URL
in the server_host parameter:



    server_host = ldaps://ldap.example.com:636





STARTTLS can be turned on with the start_tls parameter:



    start_tls = yes





Both forms require LDAP protocol version 3, which has to be set
explicitly with:



    version = 3





If any of the Postfix programs querying the map is configured in
master.cf to run chrooted, all the certificates and keys involved
have to be copied to the chroot jail. Of course, the private keys
should only be readable by the user "postfix".


The following parameters are relevant to LDAP SSL and STARTTLS:



start_tls (default: no)

Whether or not to issue STARTTLS upon connection to the
server.  Don't set this with LDAP SSL (the SSL session is setup
automatically when the TCP connection is opened).

tls_ca_cert_dir (No default; set either this or tls_ca_cert_file)

Directory containing X509 Certificate Authority certificates
in PEM format which are to be recognized by the client in
SSL/TLS connections. The files each contain one CA certificate.
The files are looked up by the CA subject name hash value,
which must hence be available. If more than one CA certificate
with the same name hash value exist, the extension must be
different (e.g. 9d66eef0.0, 9d66eef0.1 etc). The search is
performed in the ordering of the extension number, regardless
of other properties of the certificates. Use the c_rehash
utility (from the OpenSSL distribution) to create the
necessary links.

tls_ca_cert_file (No default; set either this or tls_ca_cert_dir)

File containing the X509 Certificate Authority certificates
in PEM format which are to be recognized by the client in
SSL/TLS connections. This setting takes precedence over
tls_ca_cert_dir.

tls_cert (No default; you must set this)

File containing client's X509 certificate to be used by
the client in SSL/ TLS connections.

tls_key (No default; you must set this)

File containing the private key corresponding to the above
tls_cert.

tls_require_cert (default: no)

Whether or not to request server's X509 certificate and
check its validity when establishing SSL/TLS connections.
The supported values are no and yes.


With no, the server certificate trust chain is not checked,
but with OpenLDAP prior to 2.1.13, the name in the server
certificate must still match the LDAP server name. With OpenLDAP
2.0.0 to 2.0.11 the server name is not necessarily what you
specified, rather it is determined (by reverse lookup) from the
IP address of the LDAP server connection. With OpenLDAP prior to
2.0.13, subjectAlternativeName extensions in the LDAP server
certificate are ignored: the server name must match the subject
CommonName. The no setting corresponds to the never
value of TLS_REQCERT in LDAP client configuration files.


Don't use TLS with OpenLDAP 2.0.x (and especially with x <= 11)
if you can avoid it.


With yes, the server certificate must be issued by a trusted
CA, and not be expired. The LDAP server name must match one of the
name(s) found in the certificate (see above for OpenLDAP library
version dependent behavior). The yes setting corresponds to the
demand value of TLS_REQCERT in LDAP client configuration
files.


The "try" and "allow" values of TLS_REQCERT have no equivalents
here. They are not available with OpenLDAP 2.0, and in any case have
questionable security properties. Either you want TLS verified LDAP
connections, or you don't.


The yes value only works correctly with Postfix 2.5 and later,
or with OpenLDAP 2.0. Earlier Postfix releases or later OpenLDAP
releases don't work together with this setting. Support for LDAP
over TLS was added to Postfix based on the OpenLDAP 2.0 API.

tls_random_file (No default)

Path of a file to obtain random bits from when /dev/[u]random
is not available, to be used by the client in SSL/TLS
connections.

tls_cipher_suite (No default)

Cipher suite to use in SSL/TLS negotiations.




EXAMPLE






Here's a basic example for using LDAP to look up local(8)
aliases.
Assume that in main.cf, you have:



    alias_maps = hash:/etc/aliases,
            ldap:/etc/postfix/ldap-aliases.cf





and in ldap:/etc/postfix/ldap-aliases.cf you have:



    server_host = ldap.example.com
    search_base = dc=example, dc=com





Upon receiving mail for a local address "ldapuser" that
isn't found in the /etc/aliases database, Postfix will
search the LDAP server listening at port 389 on ldap.example.com.
It will bind anonymously, search for any directory entries
whose mailacceptinggeneralid attribute is "ldapuser", read
the "maildrop" attributes of those found, and build a list
of their maildrops, which will be treated as RFC822 addresses
to which the message will be delivered.


SEE ALSO




postmap(1), Postfix lookup table manager
postconf(5), configuration parameters
mysql_table(5), MySQL lookup tables
pgsql_table(5), PostgreSQL lookup tables



README FILES






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


DATABASE_README, Postfix lookup table overview
LDAP_README, Postfix LDAP client guide



LICENSE






The Secure Mailer license must be distributed with this software.


AUTHOR(S)






Carsten Hoeger,
Hery Rakotoarisoa,
John Hensley,
Keith Stevenson,
LaMont Jones,
Liviu Daia,
Manuel Guesdon,
Mike Mattice,
Prabhat K Singh,
Sami Haahtinen,
Samuel Tardieu,
Victor Duchovni,
and many others.