LDAP SUPPORT IN POSTFIX
=======================
Postfix can use an LDAP directory as a source for any of its lookups:
aliases, virtual, canonical, etc. This allows you to keep information
for your mail service in a replicated network database with fine-grained
access controls. By not storing it locally on the mail server, the
administrators can maintain it from anywhere, and the users can control
whatever bits of it you think appropriate. You can have multiple mail
servers using the same information, without the hassle and delay of
having to copy it to each.
BUILDING WITH LDAP SUPPORT
==========================
Note: Postfix no longer supports the LDAP version 1 interface.
You need to have LDAP libraries and include files installed somewhere
on your system, and you need to configure the Postfix Makefiles
accordingly.
For example, to build the OpenLDAP libraries for use with Postfix
(i.e. LDAP client code only), you could use the following command:
% ./configure --without-kerberos --without-cyrus-sasl --without-tls \
--without-threads --disable-slapd --disable-slurpd \
--disable-debug --disable-shared
If you're using the libraries from the UM distribution
(http://www.umich.edu/~dirsvcs/ldap/ldap.html) or OpenLDAP
(http://www.openldap.org), something like this in the top level of your
Postfix source tree should work:
% make tidy
% make makefiles CCARGS="-I/usr/local/include -DHAS_LDAP" \
AUXLIBS="-L/usr/local/lib -lldap -L/usr/local/lib -llber"
On Solaris 2.x you may have to specify run-time link information,
otherwise ld.so will not find some of the shared libraries:
% make tidy
% make makefiles CCARGS="-I/usr/local/include -DHAS_LDAP" \
AUXLIBS="-L/usr/local/lib -R/usr/local/lib -lldap \
-L/usr/local/lib -R/usr/local/lib -llber"
The 'make tidy' command is needed only if you have previously built
Postfix without LDAP support.
Instead of '/usr/local' specify the actual locations of your LDAP
include files and libraries. Be sure to not mix LDAP include files
and LDAP libraries of different versions!!
If your LDAP libraries were built with Kerberos support, you'll also
need to include your Kerberos libraries in this line. Note that the KTH
Kerberos IV libraries might conflict with Postfix's lib/libdns.a, which
defines dns_lookup. If that happens, you'll probably want to link with
LDAP libraries that lack Kerberos support just to build Postfix, as it
doesn't support Kerberos binds to the LDAP server anyway. Sorry about
the bother.
If you're using one of the Netscape LDAP SDKs, you'll need to change the
AUXLIBS line to point to libldap10.so or libldapssl30.so or whatever you
have, and you may need to use the appropriate linker option (e.g. '-R')
so the executables can find it at runtime.
CONFIGURING LDAP LOOKUPS
========================
In order to use LDAP lookups, define at least one LDAP source as a table
lookup in main.cf, for example:
alias_maps = hash:/etc/aliases, ldap:ldapsource
Each LDAP source can have the following parameters, which should be
prefixed in main.cf with the name you've given the source in its
definition and an underscore. To continue the example, the first
parameter below, "server_host", would be defined in main.cf as
"ldapsource_server_host". Defaults are given in parentheses:
server_host (localhost)
The name of the host running the LDAP server, e.g.
ldapsource_server_host = ldap.your.com
It should be possible with all the libraries mentioned above to
specify multiple servers separated by spaces, with the libraries
trying them in order should the first one fail. It should also
be possible to give each server in the list a different port, by
naming them like "ldap.your.com:1444".
server_port (389)
The port the LDAP server listens on, e.g.
ldapsource_server_port = 778
search_base (No default; you must configure this.)
The base at which to conduct the search, e.g.
ldapsource_search_base = dc=your, dc=com
timeout (10 seconds)
The number of seconds a search can take before timing out, e.g.
ldapsource_timeout = 5
query_filter (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.
ldapsource_query_filter = (&(mail=%s)(paid_up=true))
result_filter (%s)
Filter applied to result attributes. Supports the same expansions
as the query_filter, and can be easily used to append (or prepend)
text.
domain (Default is to ignore this.)
This is a list of domain names, paths to files, or dictionaries.
If specified, only lookups for the domains on this list will be
performed. This means that the LDAP map won't get searched for
'user', nor will it get searched for any domain not listed. This
can significantly reduce the query load on the LDAP server.
ldapsource_domain = postfix.org, hash:/etc/postfix/searchdomains
result_attribute (maildrop)
The attribute(s) Postfix will read from any directory entries
returned by the lookup, to be resolved to an email address.
ldapsource_result_attribute = mailbox,maildrop
special_result_attribute (No default)
The attribute(s) of directory entries that can contain DNs or URLs.
If found, a recursive subsequent search is done using their values.
ldapsource_special_result_attribute = member
scope (sub)
The LDAP search scope: sub, base, or one. These translate into
LDAP_SCOPE_SUBTREE, LDAP_SCOPE_BASE, and LDAP_SCOPE_ONELEVEL.
bind (yes)
Whether or not to bind to the LDAP server. Newer LDAP
implementations don't require clients to bind, which saves
time. Example:
ldapsource_bind = no
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 ("")
If you do have to bind, do it with this distinguished name.
Example:
ldapsource_bind_dn = uid=postfix, dc=your, dc=com
bind_pw ("")
The password for the distinguished name above. If you have to
use this, you probably want to make main.cf readable only by
the Postfix user. Example:
ldapsource_bind_pw = postfixpw
cache (no)
Whether to use a client-side cache for the LDAP connection. See
ldap_enable_cache(3). It's off by default.
cache_expiry (30 seconds)
If the client-side cache is enabled, cached results will expire
after this many seconds.
cache_size (32768 bytes)
If the client-side cache is enabled, this is its size in bytes.
dereference (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 (0)
Sets (or clears) LDAP_OPT_REFERRALS (requires LDAP version 3
support.
version (2)
Specifies the LDAP protocol version to use.
debuglevel (0)
What level to set for debugging in the OpenLDAP libraries.
Don't use quotes in these variables; at least, not until the Postfix
configuration routines understand how to deal with quoted strings.
EXAMPLES
========
ALIASES
-------
Here's a basic example for using LDAP to look up aliases. Assume that in
main.cf, you have these configuration parameters defined:
alias_maps = hash:/etc/aliases, ldap:ldapsource
ldapsource_server_host = ldap.my.com
ldapsource_search_base = dc=my, 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.my.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.
VIRTUAL DOMAINS/ADDRESSES
-------------------------
If you want to keep information for virtual lookups in your directory,
it's only a little more complicated. First you need to make sure Postfix
knows about the virtual domain. An easy way to do that is to add the
domain to the mailacceptinggeneralid attribute of some entry in the
directory. Next you'll want to make sure all of your virtual recipients'
mailacceptinggeneralid attributes are fully qualified with their virtual
domains. Finally, if you want to designate a directory entry as the
default user for a virtual domain, just give it an additional
mailacceptinggeneralid (or the equivalent in your directory) of
"@virtual.dom". That's right, no user part. If you don't want a catchall
user, omit this step and mail to unknown users in the domain will simply
bounce.
If you're using a version of Postfix newer than 19991226, that should do
it. If not, you also need to add your virtual domains to relay_domains.
Simply add "$virtual_maps" to your relay_domains line. Then you can use
the same map you use to find virtual recipients to determine if a domain
is a valid virtual domain and should be allowed to relay.
In summary, you might have a catchall user for a virtual domain that
looks like this:
dn: cn=defaultrecipient, dc=fake, dc=dom
objectclass: top
objectclass: virtualaccount
cn: defaultrecipient
owner: uid=root, dc=someserver, dc=isp, dc=dom
1 -> mailacceptinggeneralid: fake.dom
2 -> mailacceptinggeneralid: @fake.dom
3 -> maildrop: realuser@real.dom
1: Postfix knows fake.dom is a valid virtual domain when it looks for
this and gets something (the maildrop) back.
2: This causes any mail for unknown users in fake.dom to go to this entry ...
3: ... and then to its maildrop.
Normal users might simply have one mailacceptinggeneralid and maildrop,
e.g. "normaluser@fake.dom" and "normaluser@real.dom".
OTHER USES
----------
Other common uses for LDAP lookups include rewriting senders and
recipients with Postfix' canonical lookups, for example in order to make
mail leaving your site appear to be coming from "First.Last@site.dom"
instead of "userid@site.dom".
NOTES AND THINGS TO THINK ABOUT
===============================
- The bits of schema and attribute names used in this document are just
examples. There's nothing special about them, other than that some are
the defaults in the LDAP configuration parameters. You can use
whatever schema you like, and configure Postfix accordingly.
- You probably want to make sure that mailacceptinggeneralids are
unique, and that not just anyone can specify theirs as postmaster or
root, say.
- An entry can have an arbitrary number of mailacceptinggeneralids or
maildrops. Maildrops can also be comma-separated lists of addresses.
They will all be found and returned by the lookups. For example, you
could define an entry intended for use as a mailing list that looks
like this (Warning! Schema made up just for this example):
dn: cn=Accounting Staff List, dc=my, dc=com
cn: Accounting Staff List
o: my.com
objectclass: maillist
mailacceptinggeneralid: accountingstaff
mailacceptinggeneralid: accounting-staff
maildrop: mylist-owner
maildrop: an-accountant
maildrop: some-other-accountant
maildrop: this, that, theother
- If you use an LDAP map for lookups other than aliases, you may have to
make sure the lookup makes sense. In the case of virtual lookups,
maildrops other than mail addresses are pretty useless, because
Postfix can't know how to set the ownership for program or file
delivery. Your query_filter should probably look something like this:
virtual_query_filter = (&(mailacceptinggeneralid=%s)(!(|(maildrop="*|*")(maildrop="*:*")(maildrop="*/*"))))
- And for that matter, even for aliases, you may not want users able to
specify their maildrops as programs, includes, etc. This might be
particularly pertinent on a "sealed" server where they don't have
local UNIX accounts, but exist only in LDAP and Cyrus. You might allow
the fun stuff only for directory entries owned by an administrative
account:
local_query_filter = (&(mailacceptinggeneralid=%s)(|(!(maildrop="*|*")(maildrop="*:*")(maildrop="*/*"))(owner=cn=root, dc=your, dc=com)))
So that if the object had a program as its maildrop and weren't owned
by "cn=root" it wouldn't be returned as a valid local user. This will
require some thought on your part to implement safely, considering the
ramifications of this type of delivery. You may decide it's not worth
the bother to allow any of that nonsense in LDAP lookups, ban it in
the query_filter, and keep things like majordomo lists in local alias
databases.
- LDAP lookups are slower than local DB or DBM lookups. For most sites
they won't be a bottleneck, but it's a good idea to know how to tune
your directory service.
FEEDBACK
========
If you have questions, send them to postfix-users@postfix.org. Please
include relevant information about your Postfix setup: LDAP-related
output from postconf, which LDAP libraries you built with, and which
directory server you're using. If your question involves your directory
contents, please include the applicable bits of some directory entries.
CREDITS
=======
Manuel Guesdon: Spotted a bug with the ldapsource_timeout attribute.
John Hensley: Multiple LDAP sources with more configurable attributes.
Carsten Hoeger: Search scope handling.
LaMont Jones: Domain restriction, URL and DN searches, multiple result
attributes.
Mike Mattice: Alias dereferencing control.
Hery Rakotoarisoa: Patches for LDAPv3 updating.
Prabhat K Singh: Wrote the initial Postfix LDAP lookups and connection caching.
Keith Stevenson: RFC 2254 escaping in queries.
Samuel Tardieu: Noticed that searches could include wildcards, prompting
the work on RFC 2254 escaping in queries. Spotted a bug
in binding.
Sami Haahtinen: Referral chasing and v3 support.
And of course Wietse.