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+PPoossttffiixx PPCCRREE SSuuppppoorrtt
+
+-------------------------------------------------------------------------------
+
+PPCCRREE ((PPeerrll CCoommppaattiibbllee RReegguullaarr EExxpprreessssiioonnss)) mmaapp ssuuppppoorrtt
+
+The optional "pcre" map type allows you to specify regular expressions with the
+PERL style notation such as \s for space and \S for non-space. The main
+benefit, however, is that pcre lookups are often faster than regexp lookups.
+This is because the pcre implementation is often more efficient than the POSIX
+regular expression implementation that you find on many systems.
+
+A description of how to use pcre tables, including examples, is given in the
+pcre_table(5) manual page. Information about PCRE itself can be found at http:/
+/www.pcre.org/.
+
+BBuuiillddiinngg PPoossttffiixx wwiitthh PPCCRREE ssuuppppoorrtt
+
+These instructions assume that you build Postfix from source code as described
+in the INSTALL document. Some modification may be required if you build Postfix
+from a vendor-specific source package.
+
+Note: to use pcre with Debian GNU/Linux's Postfix, all you need is to install
+the postfix-pcre package and you're done. There is no need to recompile
+Postfix.
+
+In some future, Postfix will have a plug-in interface for adding map types.
+Until then, you need to compile PCRE support into Postfix.
+
+First of all, you need the PCRE library (Perl Compatible Regular Expressions),
+which can be obtained from:
+
+ ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/.
+
+NOTE: pcre versions prior to 2.06 cannot be used.
+
+In order to build Postfix with PCRE support you need to add -DHAS_PCRE and a -
+I option for the PCRE include file to CCARGS, and add the path to the PCRE
+library to AUXLIBS_PCRE, for example:
+
+ make -f Makefile.init makefiles \
+ "CCARGS=-DHAS_PCRE `pcre-config --cflags`" \
+ "AUXLIBS_PCRE=`pcre-config --libs`"
+
+Postfix versions before 3.0 use AUXLIBS instead of AUXLIBS_PCRE. With Postfix
+3.0 and later, the old AUXLIBS variable still supports building a statically-
+loaded PCRE database client, but only the new AUXLIBS_PCRE variable supports
+building a dynamically-loaded or statically-loaded PCRE database client.
+
+ Failure to use the AUXLIBS_PCRE variable will defeat the purpose of dynamic
+ database client loading. Every Postfix executable file will have PCRE
+ library dependencies. And that was exactly what dynamic database client
+ loading was meant to avoid.
+
+TThhiinnggss ttoo kknnooww
+
+ * When Postfix searches a pcre: or regexp: lookup table, each pattern is
+ applied to the entire input string. 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, and "user+foo" is not broken up into user and
+ foo.
+
+ * Regular expression tables such as pcre: or regexp: are not allowed to do
+ $number substitution in lookup results that can be security sensitive:
+ currently, that restriction applies to the local aliases(5) database or the
+ virtual(8) delivery agent tables.
+