Fix #9759 SSMTP sendmail wrapper

nixos/modules/programs/ssmtp.nix

···
           Password used for SMTP auth. (STORED PLAIN TEXT, WORLD-READABLE IN NIX STORE)
         '';
       };
+      
+      setSendmail = mkOption {
+        type = types.bool;
+        default = true;
+        description = "Whether to set the system sendmail to ssmtp's.";
+      };
 
     };
 
···
       '';
 
     environment.systemPackages = [pkgs.ssmtp];
+    
+    services.mail.sendmailSetuidWrapper = mkIf networking.defaultMailServer.setSendmail {
+      program = "sendmail";
+      source = "${pkgs.ssmtp}/bin/sendmail";
+      setuid = false;
+      setgid = false;
+    };
 
   };