In this version, there are two very important functions: APIv2 and manual processing of letters with the subsequent creation of the application. For APIv2, you can learn in detail from the blog, as well as information pages:

We will stop on consideration of a functional of creation of applications from letters in more detail.

To familiarize with the functionality, we have prepared a section in the documentation at the link:

3.5.2, mail, apiv2