I do have all these things (https://github.com/Mic92/dotfiles/blob/master/nixos/eve/modu..., https://github.com/Mic92/dotfiles/blob/master/nixos/eve/modu..., https://github.com/Mic92/dotfiles/blob/master/nixos/eve/modu... ...). Especially things like ACME work a lot better the NixOS-provided curated and unit-tested acme module compared to setting up it yourself. You can also use the Nixos simple mail server setup that already provides sane defaults and puts the individual nixos modules together: https://gitlab.com/simple-nixos-mailserver/nixos-mailserver/