首先要定义一个邮件信息的基类，如下所示：

#region Properties
/// <summary>
/// Whom the message is to
/// </summary>
public virtual string To { get; set; }

/// <summary>
/// The subject of the email
/// </summary>
public virtual string Subject { get; set; }

/// <summary>
/// Whom the message is from
/// </summary>
public virtual string From { get; set; }

/// <summary>
/// Body of the text
/// </summary>
public virtual string Body { get; set; }

#endregion
}