Exchange 2013 + Outlook 2013, why is the group highlighted?

Question

Outlook

Colleagues, good afternoon.
The question was asked and I did not find the answer myself.
Why do I get a message about the number of group members in Outlook when I select a specific group as the recipient of a message?
What is this mechanism and what does Outlook hint to me? )

Answer 1

There are no pictures. Insert correctly.

Answer 2

Strange, it usually works with Yadisk.
So okay?