import NixOS' services.exim

krebs/3modules/exim.nix

@@ -0,0 +1,111 @@
+{ config, lib, pkgs, ... }:
+
+let
+  inherit (lib) mkIf mkOption singleton types;
+  inherit (pkgs) coreutils exim;
+  cfg = config.services.exim;
+in
+
+{
+
+  ###### interface
+
+  options = {
+
+    services.exim = {
+
+      enable = mkOption {
+        type = types.bool;
+        default = false;
+        description = "Whether to enable the Exim mail transfer agent.";
+      };
+
+      config = mkOption {
+        type = types.string;
+        default = "";
+        description = ''
+          Verbatim Exim configuration.  This should not contain exim_user,
+          exim_group, exim_path, or spool_directory.
+        '';
+      };
+
+      user = mkOption {
+        type = types.string;
+        default = "exim";
+        description = ''
+          User to use when no root privileges are required.
+          In particular, this applies when receiving messages and when doing
+          remote deliveries.  (Local deliveries run as various non-root users,
+          typically as the owner of a local mailbox.) Specifying this value
+          as root is not supported.
+        '';
+      };
+
+      group = mkOption {
+        type = types.string;
+        default = "exim";
+        description = ''
+          Group to use when no root privileges are required.
+        '';
+      };
+
+      spoolDir = mkOption {
+        type = types.string;
+        default = "/var/spool/exim";
+        description = ''
+          Location of the spool directory of exim.
+        '';
+      };
+
+    };
+
+  };
+
+
+  ###### implementation
+
+  config = mkIf cfg.enable {
+
+    environment = {
+      etc."exim.conf".text = ''
+        exim_user = ${cfg.user}
+        exim_group = ${cfg.group}
+        exim_path = /var/setuid-wrappers/exim
+        spool_directory = ${cfg.spoolDir}
+        ${cfg.config}
+      '';
+      systemPackages = [ exim ];
+    };
+
+    users.extraUsers = singleton {
+      name = cfg.user;
+      description = "Exim mail transfer agent user";
+      uid = config.ids.uids.exim;
+      group = cfg.group;
+    };
+
+    users.extraGroups = singleton {
+      name = cfg.group;
+      gid = config.ids.gids.exim;
+    };
+
+    security.setuidPrograms = [ "exim" ];
+
+    systemd.services.exim = {
+      description = "Exim Mail Daemon";
+      wantedBy = [ "multi-user.target" ];
+      serviceConfig = {
+        ExecStart   = "${exim}/bin/exim -bdf -q30m";
+        ExecReload  = "${coreutils}/bin/kill -HUP $MAINPID";
+      };
+      preStart = ''
+        if ! test -d ${cfg.spoolDir}; then
+          ${coreutils}/bin/mkdir -p ${cfg.spoolDir}
+          ${coreutils}/bin/chown ${cfg.user}:${cfg.group} ${cfg.spoolDir}
+        fi
+      '';
+    };
+
+  };
+
+}