What mail to create in exchange, except shared for receiving letters from the outside?

Question

Microsoft Exchange

Hello.
There is a domain, in it exchange 2010, in general, out of the box, without policies.
Problem - I can't receive emails to local mailing group addresses from external mailers. Exchange (judging by the Google report) swears at dkim.
My task is quite simple. Receive letters from external addresses on 3 mailboxes, then redirect them to a distribution group.
I want to bypass the creation of three accounts in AD, whether they are alive or disabled for shared mailboxes, and not go as far as possible into DKIM.
How to solve the problem with the least amount of time?

Answer 1

After the third paragraph, I did not understand anything, but I will try to help: By default, when creating a distribution group, only authenticated users have the right to send it, i.e. internal users. In order for the distribution group to be sent from outside - you need to tell Exchange that yes, I understand and take the risks, and uncheck it - here is how to do it: