How to set up Exchange to work with Yandex?

Question

Mail server

Installed and configured Exchange Server. The settings are almost default.
I can’t find it, I can’t understand how to set up such a mail server operation scheme (see figure): inside the organization, employees use addresses of the form [email protected], outside for clients and for access by employees from home, an address of the form [email protected] is used . Yandex mail is used for the domain. Boxes should somehow be synchronized (or duplicated).
There is a difficulty with the PTR record from the provider. That's why I'm considering this scheme.
Where, what needs to be adjusted?