From 5cd6f8e7b3f5d5bf56e407c5e79a682cb250d911 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?James=20=E2=80=98Twey=E2=80=99=20Kay?= <twey@twey.co.uk>
Date: Sat, 5 Sep 2020 21:23:15 +0100
Subject: [PATCH] Add a separate sendingFqdn option

---
 default.nix             | 28 +++++++++++++++++++++++++++-
 mail-server/postfix.nix |  2 +-
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/default.nix b/default.nix
index 6b96acd..22180ec 100644
--- a/default.nix
+++ b/default.nix
@@ -1,4 +1,3 @@
-
 #  nixos-mailserver: a simple mail server
 #  Copyright (C) 2016-2018  Robin Raymond
 #
@@ -555,6 +554,33 @@ in
       '';
     };
 
+    sendingFqdn = mkOption {
+      type = types.str;
+      default = cfg.fqdn;
+      defaultText = "config.mailserver.fqdn";
+      example = "myserver.example.com";
+      description = ''
+        The fully qualified domain name of the mail server used to
+        identify with remote servers.
+
+        If this server's IP serves purposes other than a mail server,
+        it may be desirable for the server to have a name other than
+        that to which the user will connect.  For example, the user
+        might connect to mx.example.com, but the server's IP has
+        reverse DNS that resolves to myserver.example.com; in this
+        scenario, some mail servers may reject or penalize the
+        message.
+
+        This setting allows the server to identify as
+        myserver.example.com when forwarding mail, independently of
+        `fqdn` (which, for SSL reasons, should generally be the name
+        to which the user connects).
+
+        Set this to the name to which the sending IP's reverse DNS
+        resolves.
+      '';
+    };
+
     policydSPFExtraConfig = mkOption {
       type = types.lines;
       default = "";
diff --git a/mail-server/postfix.nix b/mail-server/postfix.nix
index d3ca4fe..f41bd38 100644
--- a/mail-server/postfix.nix
+++ b/mail-server/postfix.nix
@@ -125,7 +125,7 @@ in
 
     services.postfix = {
       enable = true;
-      hostname = "${fqdn}";
+      hostname = "${sendingFqdn}";
       networksStyle = "host";
       mapFiles."valias" = valiases_file;
       mapFiles."vaccounts" = vaccounts_file;