public static void UseSmtp4dev(this IServiceCollection services)
{
SettingsStore settingsStore = new SettingsStore();
services.AddInstance <ISettingsStore>(settingsStore);
string dbDirectory = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "Smtp4dev");
Directory.CreateDirectory(dbDirectory);
FileInfo dbFile = new FileInfo(Path.Combine(dbDirectory, "Smtp4dev.db"));
MessageStore messageStore = new MessageStore(dbFile);
services.AddInstance <IMessageStore>(messageStore);
services.AddSingleton <ISmtp4devEngine, Smtp4devEngine>();
}