mailsystem: Add basic postfix configuration

mailsystem/default.nix

@@ -1,4 +1,10 @@
-{lib, ...}: {
+{
+  config,
+  lib,
+  ...
+}: let
+  cfg = config.mailsystem;
+in {
   options.mailsystem = {
     enable = lib.mkEnableOption "nixos-mailsystem";
 
@@ -14,6 +20,32 @@
       description = "Fully qualified domain name of the mail server.";
     };
 
+    reverseFqdn = lib.mkOption {
+      type = lib.types.str;
+      default = cfg.fqdn;
+      defaultText = lib.literalMD "{option}`mailsystem.fqdn`";
+      example = "server.example.com";
+      description = ''
+        Fully qualified domain name used by the server to identify
+        with other servers.
+
+        This needs to be set to the same value of the server's IP reverse DNS.
+      '';
+    };
+
+    domains = lib.mkOption {
+      type = lib.types.listOf lib.types.str;
+      example = ["example.com"];
+      default = [];
+      description = "List of domains to be served by the mail server";
+    };
+
+    messageSizeLimit = lib.mkOption {
+      type = lib.types.int;
+      default = 64 * 1024 * 1024;
+      description = "Maximum accepted mail size";
+    };
+
     vmailUID = lib.mkOption {
       type = lib.types.int;
       default = 5000;
@@ -60,6 +92,17 @@
             '';
           };
 
+          aliases = lib.mkOption {
+            type = with lib.types; listOf types.str;
+            example = ["abuse@example.com" "postmaster@example.com"];
+            default = [];
+            description = ''
+              A list of aliases of this login account.
+              Note: Use list entries like "@example.com" to create a catchAll
+              that allows sending from all email addresses in these domain.
+            '';
+          };
+
           isSystemUser = lib.mkOption {
             type = lib.types.bool;
             default = false;
@@ -83,11 +126,37 @@
       description = "All available accounts for the mailsystem.";
       default = {};
     };
+
+    extraVirtualAliases = lib.mkOption {
+      type = let
+        account = lib.mkOptionType {
+          name = "Mail Account";
+          check = account: builtins.elem account (builtins.attrNames cfg.accounts);
+        };
+      in
+        with lib.types; attrsOf (either account (nonEmptyListOf account));
+      example = {
+        "info@example.com" = "user1@example.com";
+        "postmaster@example.com" = "user1@example.com";
+        "abuse@example.com" = "user1@example.com";
+        "multi@example.com" = ["user1@example.com" "user2@example.com"];
+      };
+      description = ''
+        Virtual account aliases. A virtual alias `"info@example.com" = "user1@example.com"`
+        means that all mail to `info@example.com` is forwarded to `user1@example.com`.
+        Furthermore, it also allows the user `user1@example.com` to send emails as
+        `info@example.com`. It is also possible to create an alias for multiple accounts.
+        In this example, all mails for `multi@example.com` will be forwarded to both
+        `user1@example.com` and `user2@example.com`.
+      '';
+      default = {};
+    };
   };
 
   imports = [
     ./dovecot.nix
     ./nginx.nix
+    ./postfix.nix
     ./user.nix
   ];
 }