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+ "http://www.w3.org/TR/html4/loose.dtd">
+
+<html>
+
+<head>
+
+<title>Postfix Lookup Table Overview</title>
+
+<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
+
+</head>
+
+<body>
+
+<h1><img src="postfix-logo.jpg" width="203" height="98" ALT="">Postfix
+Lookup Table Overview</h1>
+
+<hr>
+
+<h2>Overview </h2>
+
+This document covers the following topics:
+
+<ul>
+
+<li><a href="#intro">The Postfix lookup table model</a>
+
+<li><a href="#lists">Postfix lists versus tables </a>
+
+<li><a href="#preparing">Preparing Postfix for LDAP or SQL lookups</a>
+
+<li><a href="#detect">Maintaining Postfix lookup table files</a>
+
+<li><a href="#safe_db">Updating Berkeley DB files safely</a>
+
+<li><a href="#types">Postfix lookup table types</a>
+
+</ul>
+
+<h2><a name="intro">The Postfix lookup table model</a></h2>
+
+<p> Postfix uses lookup tables to store and look up information
+for access control, address rewriting and even for content filtering.
+All Postfix lookup tables are specified as "<a href="DATABASE_README.html">type:table</a>", where
+"type" is one of the database types described under "<a
+href="#types">Postfix lookup table types</a>" at the end of this
+document, and where "table" is the lookup table name. The Postfix
+documentation uses the terms "database" and "lookup table" for the
+same thing. </p>
+
+<p> Examples of lookup tables that appear often in the Postfix
+documentation: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/<a href="postconf.5.html">main.cf</a>:
+ <a href="postconf.5.html#alias_maps">alias_maps</a> = <a href="DATABASE_README.html#types">hash</a>:/etc/postfix/aliases (local aliasing)
+ <a href="postconf.5.html#header_checks">header_checks</a> = <a href="regexp_table.5.html">regexp</a>:/etc/postfix/header_checks (content filtering)
+ <a href="postconf.5.html#transport_maps">transport_maps</a> = <a href="DATABASE_README.html#types">hash</a>:/etc/postfix/transport (routing table)
+ <a href="postconf.5.html#virtual_alias_maps">virtual_alias_maps</a> = <a href="DATABASE_README.html#types">hash</a>:/etc/postfix/virtual (address rewriting)
+</pre>
+</blockquote>
+
+<p> All Postfix lookup tables store information as (key, value)
+pairs. This interface may seem simplistic at first, but it turns
+out to be very powerful. The (key, value) query interface completely
+hides the complexities of LDAP or SQL from Postfix. This is a good
+example of connecting complex systems with simple interfaces. </p>
+
+<p> Benefits of the Postfix (key, value) query interface:</p>
+
+<ul>
+
+<li> You can implement Postfix lookup tables first with local
+Berkeley DB files and then switch to LDAP or MySQL without any
+impact on the Postfix configuration itself, as described under "<a
+href="#preparing">Preparing Postfix for LDAP or SQL lookups</a>"
+below.
+
+<li> You can use Berkeley DB files with fixed lookup strings for
+simple address rewriting operations and you can use regular expression
+tables for the more complicated work. In other words, you don't
+have to put everything into the same table.
+
+</ul>
+
+<h2><a name="lists">Postfix lists versus tables </a></h2>
+
+<p> Most Postfix lookup tables are used to look up information.
+Examples are address rewriting (the lookup string is the old address,
+and the result is the new address) or access control (the lookup
+string is the client, sender or recipient, and the result is an
+action such as "reject"). </p>
+
+<p> With some tables, however, Postfix needs to know only if the
+lookup key exists. Any non-empty lookup result value may be used
+here: the lookup result is not used. Examples
+are the <a href="postconf.5.html#local_recipient_maps">local_recipient_maps</a> that determine what local recipients
+Postfix accepts in mail from the network, the <a href="postconf.5.html#mydestination">mydestination</a> parameter
+that specifies what domains Postfix delivers locally, or the
+<a href="postconf.5.html#mynetworks">mynetworks</a> parameter that specifies the IP addresses of trusted
+clients or client networks. Technically, these are lists, not
+tables. Despite the difference, Postfix lists are described here
+because they use the same underlying infrastructure as Postfix
+lookup tables. </p>
+
+<h2><a name="preparing">Preparing Postfix for LDAP or SQL lookups</a>
+</h2>
+
+<p> LDAP and SQL are complex systems. Trying to set up both Postfix
+and LDAP or SQL at the same time is definitely not a good idea.
+You can save yourself a lot of time by implementing Postfix first
+with local files such as Berkeley DB. Local files have few surprises,
+and are easy to debug with the <a href="postmap.1.html">postmap(1)</a> command: </p>
+
+<blockquote>
+<pre>
+% <b>postmap -q info@example.com <a href="DATABASE_README.html#types">hash</a>:/etc/postfix/virtual </b>
+</pre>
+</blockquote>
+
+<p> Once you have local files working properly you can follow the
+instructions in <a href="ldap_table.5.html">ldap_table(5)</a>, <a href="mysql_table.5.html">mysql_table(5)</a>, <a href="pgsql_table.5.html">pgsql_table(5)</a>
+or <a href="sqlite_table.5.html">sqlite_table(5)</a>
+and replace local file lookups with LDAP or SQL lookups. When you
+do this, you should use the <a href="postmap.1.html">postmap(1)</a> command again, to verify
+that database lookups still produce the exact same results as local
+file lookup: </p>
+
+<blockquote>
+<pre>
+% <b>postmap -q info@example.com <a href="ldap_table.5.html">ldap</a>:/etc/postfix/virtual.cf </b>
+</pre>
+</blockquote>
+
+<p> Be sure to exercise all the partial address or parent domain
+queries that are documented under "table search order" in the
+relevant manual page: <a href="access.5.html">access(5)</a>, <a href="canonical.5.html">canonical(5)</a>, <a href="virtual.5.html">virtual(5)</a>,
+<a href="transport.5.html">transport(5)</a>, or under the relevant configuration parameter:
+<a href="postconf.5.html#mynetworks">mynetworks</a>, <a href="postconf.5.html#relay_domains">relay_domains</a>, <a href="postconf.5.html#parent_domain_matches_subdomains">parent_domain_matches_subdomains</a>. </p>
+
+<h2><a name="detect">Maintaining Postfix lookup table files</a></h2>
+
+<p> When you make changes to a database while the mail system is
+running, it would be desirable if Postfix avoids reading information
+while that information is being changed. It would also be nice if
+you can change a database without having to execute "postfix reload",
+in order to force Postfix to use the new information. Each time
+you do "postfix reload" Postfix loses a lot of performance.
+</p>
+
+<ul>
+
+<li> <p> If you change a network database such as LDAP, NIS or
+SQL, there is no need to execute "postfix reload". The LDAP, NIS
+or SQL server takes care of read/write access conflicts and gives
+the new data to Postfix once that data is available. </p>
+
+<li> <p> If you change a <a href="regexp_table.5.html">regexp</a>:, <a href="pcre_table.5.html">pcre</a>:, <a href="cidr_table.5.html">cidr</a>: or <a href="DATABASE_README.html#types">texthash</a>: file
+then Postfix
+may not pick up the file changes immediately. This is because a
+Postfix process reads the entire file into memory once and never
+examines the file again. </p>
+
+<ul>
+
+<li> <p> If the file is used by a short-running process such as
+<a href="smtpd.8.html">smtpd(8)</a>, <a href="cleanup.8.html">cleanup(8)</a> or <a href="local.8.html">local(8)</a>, there is no need to execute
+"postfix reload" after making a change. </p>
+
+<li> <p> If the file is being used by a long-running process such
+as <a href="trivial-rewrite.8.html">trivial-rewrite(8)</a> on a busy server it may be necessary to
+execute "postfix reload". </p>
+
+</ul>
+
+<li> <p> If you change a local file based database such as DBM or
+Berkeley DB, there is no need to execute "postfix reload". Postfix
+uses file locking to avoid read/write access conflicts, and whenever
+a Postfix daemon process notices that a file has changed it will
+terminate before handling the next client request, so that a new
+process can initialize with the new database. </p>
+
+</ul>
+
+<h2><a name="safe_db">Updating Berkeley DB files safely</a></h2>
+
+<p> Postfix uses file locking to avoid access conflicts while
+updating Berkeley DB or other local database files. This used to
+be safe, but as Berkeley DB has evolved to use more aggressive
+caching, file locking may no longer be sufficient. </p>
+
+<p> Furthermore, file locking would not prevent problems when the
+update fails because the disk is full or something else causes a
+database update to fail. In particular, commands such as <a href="postmap.1.html">postmap(1)</a>
+or <a href="postalias.1.html">postalias(1)</a> overwrite existing files. If the overwrite
+fails in the middle then you have no usable database, and Postfix
+will stop working. This is not an issue with the CDB database type
+available with Postfix 2.2 and later: <a href="CDB_README.html">CDB</a>
+creates a new file, and renames the file upon successful completion.
+</p>
+
+<p> With Berkeley DB and other "one file" databases, it is
+possible to add some extra robustness by using "mv" to REPLACE an
+existing database file instead of overwriting it: </p>
+
+<blockquote>
+<pre>
+# <b>postmap access.in &amp;&amp; mv access.in.db access.db</b>
+</pre>
+</blockquote>
+
+<p> This converts the input file "access.in" into the output file
+"access.in.db", and replaces the file "access.db" only when the
+<a href="postmap.1.html">postmap(1)</a> command was successful. Of course typing such commands
+becomes boring quickly, and this is why people use "make" instead,
+as shown below. User input is shown in bold font. </p>
+
+<blockquote>
+<pre>
+# <b>cat Makefile</b>
+all: aliases.db access.db virtual.db ...etcetera...
+
+# Note 1: commands are specified after a TAB character.
+# Note 2: use <a href="postalias.1.html">postalias(1)</a> for local aliases, <a href="postmap.1.html">postmap(1)</a> for the rest.
+aliases.db: aliases.in
+ postalias aliases.in
+ mv aliases.in.db aliases.db
+
+access.db: access.in
+ postmap access.in
+ mv access.in.db access.db
+
+virtual.db: virtual.in
+ postmap virtual.in
+ mv virtual.in.db virtual.db
+
+...etcetera...
+# <b>vi access.in</b>
+...editing session not shown...
+# <b>make</b>
+postmap access.in
+mv access.in.db access.db
+#
+</pre>
+</blockquote>
+
+<p> The "make" command updates only the files that have changed.
+In case of error, the "make" command will stop and will not invoke
+the "mv" command, so that Postfix will keep using the existing
+database file as if nothing happened. </p>
+
+<h2><a name="types">Postfix lookup table types</a> </h2>
+
+<p> To find out what database types your Postfix system supports,
+use the "<b>postconf -m</b>" command. Here is a list of database types
+that are often supported: </p>
+
+<blockquote>
+
+<dl>
+
+<dt> <b>btree</b> </dt>
+
+<dd> A sorted, balanced tree structure. This is available only on
+systems with support for Berkeley DB databases. Database files are
+created with the <a href="postmap.1.html">postmap(1)</a> or <a href="postalias.1.html">postalias(1)</a> command. The lookup
+table name as used in "<a href="DATABASE_README.html#types">btree</a>:table" is the database file name
+without the ".db" suffix. </dd>
+
+<dt> <b>cdb</b> </dt>
+
+<dd> A read-optimized structure with no support for incremental updates.
+Database files are created with the <a href="postmap.1.html">postmap(1)</a> or <a href="postalias.1.html">postalias(1)</a> command.
+The lookup table name as used in "<a href="CDB_README.html">cdb</a>:table" is the database file name
+without the ".cdb" suffix. This feature is available with Postfix 2.2
+and later. </dd>
+
+<dt> <b>cidr</b> </dt>
+
+<dd> A table that associates values with Classless Inter-Domain
+Routing (CIDR) patterns. The table format is described in <a href="cidr_table.5.html">cidr_table(5)</a>.
+</dd>
+
+<dt> <b>dbm</b> </dt>
+
+<dd> An indexed file type based on hashing. This is available only
+on systems with support for DBM databases. Public database files
+are created with the <a href="postmap.1.html">postmap(1)</a> or <a href="postalias.1.html">postalias(1)</a> command, and private
+databases are maintained by Postfix daemons. The lookup table name
+as used in "<a href="DATABASE_README.html#types">dbm</a>:table" is the database file name without the ".dir"
+or ".pag" suffix. </dd>
+
+<dt> <b>environ</b> </dt>
+
+<dd> The UNIX process environment array. The lookup key is the
+variable name. The lookup table name in "<a href="DATABASE_README.html#types">environ</a>:table" is ignored.
+</dd>
+
+<dt> <b>fail</b> </dt>
+
+<dd> A table that reliably fails all requests. The lookup table
+name is used for logging only. This table exists to simplify Postfix
+error tests. </dd>
+
+<dt> <b>hash</b> </dt>
+
+<dd> An indexed file type based on hashing. This is available only
+on systems with support for Berkeley DB databases. Public database
+files are created with the <a href="postmap.1.html">postmap(1)</a> or <a href="postalias.1.html">postalias(1)</a> command, and
+private databases are maintained by Postfix daemons. The database
+name as used in "<a href="DATABASE_README.html#types">hash</a>:table" is the database file name without the
+".db" suffix. </dd>
+
+<dt> <b>inline</b> (read-only) </dt>
+
+<dd> A non-shared, in-memory lookup table. Example: "<a href="DATABASE_README.html#types">inline</a>:{
+<i>key=value</i>, { <i>key = text with whitespace or comma</i> }}".
+Key-value pairs are separated by whitespace or comma; with a key-value
+pair inside "{}", whitespace is ignored after the opening "{",
+around the "=" between key and value, and before the closing "}".
+Inline tables eliminate the
+need to create a database file for just a few fixed elements. See
+also the <a href="DATABASE_README.html#types">static</a>: map type. </dd>
+
+<dt> <b>internal</b> </dt>
+
+<dd> A non-shared, in-memory hash table. Its content are lost when
+a process terminates. </dd>
+
+<dt> <b>lmdb</b> </dt>
+
+<dd> OpenLDAP LMDB database. This is available only on systems
+with support for LMDB databases. Public database files are created
+with the <a href="postmap.1.html">postmap(1)</a> or <a href="postalias.1.html">postalias(1)</a> command, and private databases
+are maintained by Postfix daemons. The database name as used in
+"<a href="lmdb_table.5.html">lmdb</a>:table" is the database file name without the ".lmdb" suffix.
+See <a href="lmdb_table.5.html">lmdb_table(5)</a> for details. </dd>
+
+<dt> <b>ldap</b> (read-only) </dt>
+
+<dd> LDAP database client. Configuration details are given in the
+<a href="ldap_table.5.html">ldap_table(5)</a>. </dd>
+
+<dt> <b>memcache</b> </dt>
+
+<dd> Memcache database client. Configuration details are given in
+<a href="memcache_table.5.html">memcache_table(5)</a>. </dd>
+
+<dt> <b>mysql</b> (read-only) </dt>
+
+<dd> MySQL database client. Configuration details are given in
+<a href="mysql_table.5.html">mysql_table(5)</a>. </dd>
+
+<dt> <b>netinfo</b> (read-only) </dt>
+
+<dd> Netinfo database client. </dd>
+
+<dt> <b>nis</b> (read-only) </dt>
+
+<dd> NIS database client. </dd>
+
+<dt> <b>nisplus</b> (read-only) </dt>
+
+<dd> NIS+ database client. Configuration details are given in
+<a href="nisplus_table.5.html">nisplus_table(5)</a>. </dd>
+
+<dt> <b>pcre</b> (read-only) </dt>
+
+<dd> A lookup table based on Perl Compatible Regular Expressions.
+The file format is described in <a href="pcre_table.5.html">pcre_table(5)</a>. The lookup table
+name as used in "<a href="pcre_table.5.html">pcre</a>:table" is the name of the regular expression
+file. </dd>
+
+<dt> <b>pipemap</b> (read-only) </dt>
+
+<dd> A pipeline of lookup tables. Example:
+"<a href="DATABASE_README.html#types">pipemap</a>:{<i>type<sub>1</sub>:name<sub>1</sub>, ...,
+type<sub>n</sub>:name<sub>n</sub></i>}". Each "<a href="DATABASE_README.html#types">pipemap</a>:" query is
+given to the first table. Each lookup result becomes the query for
+the next table in the pipeline, and the last table produces the
+final result. When any table lookup produces no result, the pipeline
+produces no result. The first and last characters of the "<a href="DATABASE_README.html#types">pipemap</a>:"
+table name must be "{" and "}". Within these, individual maps are
+separated with comma or whitespace. </dd>
+
+<dt> <b>pgsql</b> (read-only) </dt>
+
+<dd> PostgreSQL database client. Configuration details are given
+in <a href="pgsql_table.5.html">pgsql_table(5)</a>. </dd>
+
+<dt> <b>proxy</b> </dt>
+
+<dd> Postfix <a href="proxymap.8.html">proxymap(8)</a> client for shared access to Postfix
+databases. The lookup table name syntax is "<a href="proxymap.8.html">proxy</a>:<a href="DATABASE_README.html">type:table</a>".
+</dd>
+
+<dt> <b>randmap</b> (read-only) </dt>
+
+<dd> An in-memory table that performs random selection. Example:
+"<a href="DATABASE_README.html#types">randmap</a>:{<i>result<sub>1</sub>. ..., result<sub>n</sub></i>}".
+Each table query returns a random choice from the specified results.
+The first and last characters of the "<a href="DATABASE_README.html#types">randmap</a>:" table name must be
+"{" and "}". Within these, individual maps are separated with comma
+or whitespace. To give a specific result more weight, specify it
+multiple times. </dd>
+
+<dt> <b>regexp</b> (read-only) </dt>
+
+<dd> A lookup table based on regular expressions. The file format
+is described in <a href="regexp_table.5.html">regexp_table(5)</a>. The lookup table name as used in
+"<a href="regexp_table.5.html">regexp</a>:table" is the name of the regular expression file. </dd>
+
+<dt> <b>sdbm</b> </dt>
+
+<dd> An indexed file type based on hashing. This is available only
+on systems with support for SDBM databases. Public database files
+are created with the <a href="postmap.1.html">postmap(1)</a> or <a href="postalias.1.html">postalias(1)</a> command, and private
+databases are maintained by Postfix daemons. The lookup table name
+as used in "<a href="DATABASE_README.html#types">sdbm</a>:table" is the database file name without the ".dir"
+or ".pag" suffix. </dd>
+
+<dt> <b>socketmap</b> (read-only) </dt>
+
+<dd> Sendmail-style socketmap client. The name of the table is
+either <b>inet</b>:<i>host</i>:<i>port</i>:<i>name</i> for a TCP/IP
+server, or <b>unix</b>:<i>pathname</i>:<i>name</i> for a UNIX-domain
+server. See <a href="socketmap_table.5.html">socketmap_table(5)</a> for details. </dd>
+
+<dt> <b>sqlite</b> (read-only) </dt>
+
+<dd> SQLite database. Configuration details are given in <a href="sqlite_table.5.html">sqlite_table(5)</a>.
+</dd>
+
+<dt> <b>static</b> (read-only) </dt>
+
+<dd> A table that always returns its name as the lookup result.
+For example, "<a href="DATABASE_README.html#types">static</a>:foobar" always returns the string "foobar" as
+lookup result. Specify "<a href="DATABASE_README.html#types">static</a>:{ <i>text with whitespace</i> }"
+when the result contains whitespace; this form ignores whitespace
+after the opening "{" and before the closing "}". See also the
+<a href="DATABASE_README.html#types">inline</a>: map type. </dd>
+
+<dt> <b>tcp</b> </dt>
+
+<dd> TCP/IP client. The protocol is described in <a href="tcp_table.5.html">tcp_table(5)</a>. The
+lookup table name is "<a href="tcp_table.5.html">tcp</a>:host:port" where "host" specifies a
+symbolic hostname or a numeric IP address, and "port" specifies a
+symbolic service name or a numeric port number. </dd>
+
+<dt> <b>texthash</b> (read-only) </dt>
+
+<dd> A table that produces similar results as <a href="DATABASE_README.html#types">hash</a>: files, except
+that you don't have to run the <a href="postmap.1.html">postmap(1)</a> command before you can
+use the file, and that <a href="DATABASE_README.html#types">texthash</a>: does not detect changes after the
+file is read. The lookup table name is "<a href="DATABASE_README.html#types">texthash</a>:filename", where
+the file name is taken literally; no suffix is appended. </dd>
+
+<dt> <b>unionmap</b> (read-only) </dt>
+
+<dd> A table that sends each query to multiple lookup tables and
+that concatenates all found results, separated by comma. The table
+name syntax is the same as for pipemap tables. </dd>
+
+<dt> <b>unix</b> (read-only) </dt>
+
+<dd> A limited view of the UNIX authentication database. The following
+tables are implemented:
+
+<dl>
+
+<dt> <b>unix:passwd.byname</b> </dt>
+
+<dd>The table is the UNIX password database. The key is a login
+name. The result is a password file entry in passwd(5) format.
+</dd>
+
+<dt> <b>unix:group.byname</b> </dt>
+
+<dd> The table is the UNIX group database. The key is a group name.
+The result is a group file entry in group(5) format. </dd>
+
+</dl> </dd>
+
+</dl>
+
+</blockquote>
+
+<p> Other lookup table types may be available depending on how
+Postfix was built. With some Postfix distributions the list is
+dynamically extensible as support for lookup tables is dynamically
+linked into Postfix. </p>
+
+</body>
+
+</html>