diff --git a/nixos/modules/services/mail/postfix.nix b/nixos/modules/services/mail/postfix.nix
index d7378821440d38..356ac32139e9c9 100644
--- a/nixos/modules/services/mail/postfix.nix
+++ b/nixos/modules/services/mail/postfix.nix
@@ -612,10 +612,7 @@ in
     {
 
       environment = {
-        etc = singleton
-          { source = "/var/lib/postfix/conf";
-            target = "postfix";
-          };
+        etc."postfix".source = "/var/lib/postfix/conf";
 
         # This makes it comfortable to run 'postqueue/postdrop' for example.
         systemPackages = [ pkgs.postfix ];
diff --git a/pkgs/servers/mail/postfix/default.nix b/pkgs/servers/mail/postfix/default.nix
index c0e6252a5518c1..60a976543d49a2 100644
--- a/pkgs/servers/mail/postfix/default.nix
+++ b/pkgs/servers/mail/postfix/default.nix
@@ -1,6 +1,7 @@
 { stdenv, lib, fetchurl, makeWrapper, gnused, db, openssl, cyrus_sasl, libnsl
 , coreutils, findutils, gnugrep, gawk, icu, pcre, m4
 , buildPackages
+, nixosTests
 , withLDAP ? true, openldap
 , withPgSQL ? false, postgresql
 , withMySQL ? false, libmysqlclient
@@ -85,6 +86,8 @@ in stdenv.mkDerivation rec {
 
   installFlags = [ "install_root=installdir" ];
 
+  passthru.tests.dovecot = nixosTests.dovecot;
+
   postInstall = ''
     mkdir -p $out
     mv -v installdir/$out/* $out/