MailTool/MailFromWho/Program.cs

using MailFromWho;
using Microsoft.Extensions.Configuration;

IConfiguration config = new ConfigurationBuilder()
    .AddJsonFile("appsettings.json")
    .Build();

Settings settings = config.GetRequiredSection("Settings").Get<Settings>();

new Imap(settings).GetAllAddresses();
new Format(settings).CreateCSV();