From 5d169c3ef29fcff2951b107a9fd2bd9e7b16c2fe Mon Sep 17 00:00:00 2001
From: Robin Raymond <robin@robinraymond.de>
Date: Fri, 23 Feb 2018 14:56:28 +0100
Subject: [PATCH] fixes #88

---
 mail-server/systemd.nix | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/mail-server/systemd.nix b/mail-server/systemd.nix
index a59e8ce..e009f44 100644
--- a/mail-server/systemd.nix
+++ b/mail-server/systemd.nix
@@ -41,9 +41,13 @@ let
   createDhParameterFile =
     ''
       # Create a dh parameter file
-      ${pkgs.openssl}/bin/openssl \
-            dhparam ${builtins.toString cfg.dhParamBitLength} \
-            > "${cfg.certificateDirectory}/dh.pem"
+      if [ ! -f "''${cfg.certificateDirectory}/dh.pem" ]
+      then
+          mkdir -p "${cfg.certificateDirectory}"
+          ${pkgs.openssl}/bin/openssl \
+                dhparam ${builtins.toString cfg.dhParamBitLength} \
+                > "${cfg.certificateDirectory}/dh.pem"
+      fi
     '';
 
   createDomainDkimCert = dom: