Postfix PCRE Support
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
https://www.pcre.org/.