pull nixos-mailserver module into this repo

nixos-mailserver/sieve-after.nix

@@ -0,0 +1,20 @@
+{ stdenv, dovecot_pigeonhole}:
+
+stdenv.mkDerivation rec {
+  name = "sieve-after";
+
+  src = ./sieve-after;
+
+  phases = [ "copyPhase" "compilePhase" ];
+
+  copyPhase = ''
+    cd $src
+    mkdir $out
+    cp -Rv $src/. $out/
+    find $out -type d -exec chmod -c 0755 {} \;
+    set +x
+    '';
+  compilePhase = ''
+    find $out -iname '*.sieve' -print0 | xargs -t -0 -n1 ${dovecot_pigeonhole}/bin/sievec -c /dev/null
+  '';
+}