postfix service: don't empty local_recipient_maps

From Postfix documentation:

With this setting, the Postfix SMTP server will not reject mail with "User
unknown in local recipient table". Don't do this on systems that receive mail
directly from the Internet. With today's worms and viruses, Postfix will become
a backscatter source: it accepts mail for non-existent recipients and then
tries to return that mail as "undeliverable" to the often forged sender
address.

nixos/doc/manual/release-notes/rl-1703.xml

@@ -46,6 +46,7 @@ following incompatible changes:</para>
       for what those parameters represent.
     </para>
   </listitem>
+
   <listitem>
     <para>
       <literal>ansible</literal> now defaults to ansible version 2 as version 1
@@ -54,6 +55,7 @@ following incompatible changes:</para>
       vulnerability</link> unpatched by upstream.
     </para>
   </listitem>
+
   <listitem>
     <para>
       <literal>gnome</literal> alias has been removed along with
@@ -116,7 +118,6 @@ following incompatible changes:</para>
   </listitem>
 
   <listitem>
-
     <para><literal>overridePackages</literal> function no longer exists.
     It is replaced by <link
     xlink:href="https://nixos.org/nixpkgs/manual/#sec-overlays-install">
@@ -153,6 +154,15 @@ following incompatible changes:</para>
     </para>
   </listitem>
 
+  <listitem>
+    <para>
+      <literal>local_recipient_maps</literal> is not set to empty value by
+      Postfix service. It's an insecure default as stated by Postfix
+      documentation. Those who want to retain this setting need to set it via
+      <literal>services.postfix.extraConfig</literal>.
+    </para>
+  </listitem>
+
 </itemizedlist>
 
 

nixos/modules/services/mail/postfix.nix

@@ -79,8 +79,6 @@ let
       relay_domains = ${concatStringsSep ", " cfg.relayDomains}
     ''
     + ''
-      local_recipient_maps =
-
       relayhost = ${if cfg.lookupMX || cfg.relayHost == "" then
           cfg.relayHost
         else