diff --git a/nixbld-etc-nixos/configuration.nix b/nixbld-etc-nixos/configuration.nix
index 85575b12..9457f433 100644
--- a/nixbld-etc-nixos/configuration.nix
+++ b/nixbld-etc-nixos/configuration.nix
@@ -764,6 +764,8 @@ in
     ownerEmail = "sb" + "@m-labs.hk";
     commentAddress = "helpdesk" + "@m-labs.hk";
     correspondAddress = "helpdesk" + "@m-labs.hk";
+    sendmailPath = "${pkgs.msmtp}/bin/msmtp";
+    sendmailArguments = ["-t" "-C" "/etc/nixos/secret/rt_msmtp.conf"];
   };
 
   system.stateVersion = "21.05";
diff --git a/nixbld-etc-nixos/rt.nix b/nixbld-etc-nixos/rt.nix
index 730dbbc0..74045c5e 100644
--- a/nixbld-etc-nixos/rt.nix
+++ b/nixbld-etc-nixos/rt.nix
@@ -35,10 +35,11 @@ let
       Set($OwnerEmail, '${cfg.ownerEmail}');
       Set($MaxAttachmentSize, 15360000);
       Set($CheckMoreMSMailHeaders, 1);
+      Set($RTAddressRegexp, '^(helpdesk|sales)\@(m-labs.hk)$');
       Set($LoopsToRTOwner, 0);
 
       # System (Outgoing mail)
-      Set($SetOutgoingMailFrom, '${cfg.ownerEmail}');
+      Set($SetOutgoingMailFrom, 'helpdesk@m-labs.hk');
 
       # System (Sendmail configuration)
       Set($SendmailPath, '${cfg.sendmailPath}');