public abstract class EmailProvider : ProviderBase

    {

          #region Public Methods and Operators

        public abstract EmailResponse SendEmail(ApiSetting apiSetting, EmailContent content);

          #endregion

    }

public sealed class EmailProviderCollection : ProviderCollection

    {

        #region Public Indexers

        public new EmailProvider this[string name]

        {

            get { return (EmailProvider) base[name]; }

        }

        #endregion

    }

 public sealed class EmailProviderConfiguration : ConfigurationSection

    {

        #region Public Properties

        /// <summary>

        ///     Gets the default provider name.

        /// </summary>

        [ConfigurationProperty("default", DefaultValue = "EDMProvider")]

        public string DefaultProviderName

        {

            get { return base["default"] as string; }

        }

        /// <summary>

        ///     Gets the providers.

        /// </summary>

        [ConfigurationProperty("providers")]

        public ProviderSettingsCollection Providers

        {

            get { return (ProviderSettingsCollection) base["providers"]; }

        }

        #endregion

    }

 public static class EmailProviderManager

    {

        #region Static Fields

        private static readonly EmailProviderCollection Providers = new EmailProviderCollection();

        #endregion

        #region Constructors and Destructors

        /// <summary>

        ///     Initializes static members of the <see cref="EmailProviderConfiguration" /> class.

        /// </summary>

        static EmailProviderManager()

        {

            Initialize();

        }

        #endregion

        #region Public Properties

        /// <summary>

        ///     Gets the default.

        /// </summary>

        public static EmailProvider EmailProvider { get; private set; }

        #endregion

        #region Methods

        /// <summary>

        ///     Reads the configuration related to the set of configured

        ///     providers and sets the default and collection of providers and settings.

        /// </summary>

        private static void Initialize()

        {

            try

            {

                var section = (EmailProviderConfiguration) ConfigurationManager.GetSection("EmailProviders");

                if (section == null)

                {

                    throw new ConfigurationErrorsException("Email Provider Section is not set");

                }

                ProvidersHelper.InstantiateProviders(section.Providers, Providers, typeof (EmailProvider));

                if (Providers[section.DefaultProviderName] == null)

                {

                    throw new ConfigurationErrorsException("Email provider is not set");

                }

                EmailProvider = Providers[section.DefaultProviderName];

            }

            catch (Exception ex)

            {

                Log.Debug(ex.Message, ex);

            }

        }

  public sealed class EDMProvider : EmailProvider

    {

        #region Public Methods and Operators

        public override EmailResponse SendEmail(ApiSetting apiSetting, EmailContent content)

        {

           。。。。

      }

}

<configuration xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">

  <configSections>

    <section name="EmailProviders" type="AAA.Mail.Configuration.EmailProviderConfiguration, AAA.Mail" />

  </configSections>

  <EmailProviders default="EDMProvider">

    <providers>

      <add name="EDMProvider" type="AAA.Mail.EDM.EDMProvider, AAA.Mail.EDM" />

    </providers>

  </EmailProviders>

</configuration>