There are currently two different ways to install software on NixOS. One is declarative and the other more imperative.
pkgs.neomutt into your
configuration.nix like this:
environment.systemPackages = [ pkgs.neomutt ];
For further reference, you might want to read the nixOS manual.
You just have to run
nix-env -iA nixos.neomutt
Alternatively, you can also install a more modern version from NixOS unstable, even when you’re running NixOS stable.
nix-env -f https://github.com/NixOS/nixpkgs-channels/archive/nixos-unstable.tar.gz -iA neomutt
Due to the isolated nature of nix package management, you don’t run into trouble.
To update a particular package, run
nix-env -u neomutt
To remove a particular package, run
nix-env -e neomutt
nix-shell '<nixpkgs>' -A neomutt
That will install all build dependencies and put you into a shell where every needed environment variable is already set. For further information, you may want to consult the nix-shell manual.
Now you can follow the guide for building NeoMutt.
These instructions will help you install all the dependencies you’ll need to debug NeoMutt.
Now you can follow the guide for debugging NeoMutt.