dovecot: fix fts_flatcurve linking errors

1. "Undefined symbols" errors were caused by wrong linker flags being used for plugin builds
   on darwin.
2. Openssl build error surfaced on darwin machines with sandboxing being enabled. This is fixed by disabling sandboxing
   on darwin machines.

pkgs/by-name/do/dovecot/generic.nix

@@ -4,6 +4,7 @@
   patches,
 }:
 {
+  autoreconfHook,
   stdenv,
   lib,
   fetchzip,
@@ -64,7 +65,8 @@ stdenv.mkDerivation (finalAttrs: {
     perl
     pkg-config
   ]
-  ++ lib.optionals (stdenv.hostPlatform.isLinux && !stdenv.hostPlatform.isDarwin) [ rpcsvc-proto ];
+  ++ lib.optionals (stdenv.hostPlatform.isLinux && !stdenv.hostPlatform.isDarwin) [ rpcsvc-proto ]
+  ++ lib.optionals (stdenv.hostPlatform.isDarwin) [ autoreconfHook ];
 
   buildInputs = [
     openssl
@@ -137,6 +139,12 @@ stdenv.mkDerivation (finalAttrs: {
   )
   + lib.optionalString stdenv.hostPlatform.isLinux ''
     export systemdsystemunitdir=$out/etc/systemd/system
+  ''
+  + lib.optionalString stdenv.hostPlatform.isDarwin ''
+    substituteInPlace configure.ac \
+    --replace-fail \
+      'NOPLUGIN_LDFLAGS="-no-undefined"' \
+      'NOPLUGIN_LDFLAGS="-undefined dynamic_lookup"'
   '';
 
   preBuild = lib.optionalString (lib.strings.versionOlder version "2.4" && stdenv.isDarwin) ''
@@ -203,7 +211,6 @@ stdenv.mkDerivation (finalAttrs: {
   strictDeps = true;
 
   meta = {
-    broken = lib.versionAtLeast version "2.4" && stdenv.hostPlatform.isDarwin; # fails to link openssl
     homepage = "https://dovecot.org/";
     description = "Open source IMAP and POP3 email server written with security primarily in mind";
     license = with lib.licenses; [