How to mark a method as deprecated?

In computer software standards and documentation, the term deprecation is applied to software features that are superseded and should be avoided. Although deprecated features remain in the current version, their use may raise warning messages recommending alternate practices, and deprecation may indicate that the feature will be removed in the future. Features are deprecated—rather than being removed to provide backward compatibility and give programmers using the feature time to bring their code into compliance with the new standard. You can mark your own methods as deprecated:

[Obsolete("Use New Version with Textonly email version")]
public DataTable GetReminderEmailsForToday()
{
    ....
}