The Classic Mail Handler has been deprecated in version 9.2.0. Classic Mail Handlers have been available in Email This Issue for many years. Handlers of this type follow the traditional ways of configuration: there are fields and options in a single entity to configure the behavior of the handler.
The new Next Generation Mail Handlers come along with Email This Issue's Mail Account management. Handlers of this type are composed of building blocks (actions). It takes algorithmic thinking to build up these handlers but they are ultimately simpler and more flexible.
There are several reasons why you should for the Next Generation of Mail Handlers. See the following table for a quick comparison of the two types of handlers: