It is a configuration to use git sendemail with gmail in NixOS.

configuration.nix

...

  home-manager.users.userid = {
    programs.git = {
      enable = true;
      package = pkgs.gitAndTools.gitFull;
      userName  = "Your Name";
      userEmail = "your@gmail.com";
      extraConfig = {
        sendemail = {
          smtpserver = "smtp.gmail.com";
          smtpuser = "your@gmail.com";
          smtpencryption = "tls";
          smtpserverport = 587;
          smtpPass = "yourpassword";
        };
      };
    };
  };
  
...