C#: What are options pattern and IOptions<T>?

1public class EmailSettings
2{
3    public string SmtpServer { get; set; }
4    public int Port { get; set; }
5    public bool UseSsl { get; set; }
6}

1{
2  "EmailSettings": {
3    "SmtpServer": "smtp.gmail.com",
4    "Port": 587,
5    "UseSsl": true
6  }
7}

1builder.Services.Configure<EmailSettings>(
2    builder.Configuration.GetSection("EmailSettings"));

1public class EmailService
2{
3    private readonly EmailSettings _settings;
4
5    public EmailService(IOptions<EmailSettings> options)
6    {
7        _settings = options.Value;
8    }
9}

1builder.Services.AddOptions<EmailSettings>()
2    .Bind(builder.Configuration.GetSection("EmailSettings"))
3    .ValidateDataAnnotations()
4    .ValidateOnStart();