nixos/sympa: fix outgoing messaging
nixos/sympa: fix outgoing messaging

Because ProtectKernelModules implies NoNewPrivileges, postfix's sendmail
executable, which is setgid, wasn't able to send mail.

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs