diff --git a/nixos/modules/programs/ssmtp.nix b/nixos/modules/programs/ssmtp.nix
index 34eafd4fa846..7b00efbb4686 100644
--- a/nixos/modules/programs/ssmtp.nix
+++ b/nixos/modules/programs/ssmtp.nix
@@ -20,6 +20,7 @@ in
     networking.defaultMailServer = {
 
       directDelivery = mkOption {
+        type = types.bool;
         default = false;
         example = true;
         description = ''
@@ -35,6 +36,7 @@ in
       };
 
       hostName = mkOption {
+        type = types.str;
         example = "mail.example.org";
         description = ''
           The host name of the default mail server to use to deliver
@@ -42,7 +44,17 @@ in
         '';
       };
 
+      root = mkOption {
+        type = types.str;
+        default = "";
+        example = "root@example.org";
+        description = ''
+          The e-mail to which mail for users with UID < 1000 is forwarded.
+        '';
+      };
+
       domain = mkOption {
+        type = types.str;
         default = "";
         example = "example.org";
         description = ''
@@ -51,6 +63,7 @@ in
       };
 
       useTLS = mkOption {
+        type = types.bool;
         default = false;
         example = true;
         description = ''
@@ -60,6 +73,7 @@ in
       };
 
       useSTARTTLS = mkOption {
+        type = types.bool;
         default = false;
         example = true;
         description = ''
@@ -70,6 +84,7 @@ in
       };
 
       authUser = mkOption {
+        type = types.str;
         default = "";
         example = "foo@example.org";
         description = ''
@@ -78,6 +93,7 @@ in
       };
 
       authPass = mkOption {
+        type = types.str;
         default = "";
         example = "correctHorseBatteryStaple";
         description = ''
@@ -96,6 +112,7 @@ in
       ''
         MailHub=${cfg.hostName}
         FromLineOverride=YES
+        ${if cfg.root != "" then "root=${cfg.root}" else ""}
         ${if cfg.domain != "" then "rewriteDomain=${cfg.domain}" else ""}
         UseTLS=${if cfg.useTLS then "YES" else "NO"}
         UseSTARTTLS=${if cfg.useSTARTTLS then "YES" else "NO"}