As per security policy in Exchange Server of our organization, Sender from outside cannot be able to send mail to internal mail distribution group. However, We want to make an exception in the policy so that:

Sender from a specific domain can be able to send mail in our Internal Email distribution group (we also want keep this access limited to 10-15 internal email group maximum; not to all mail group in my forest)

but we are unable to configure as per the requirement. it would be great if someone help me in this regard.

BR//

Jubayer

By default Distribution groups are set to receive emails only from authenticated users, you can change that to receive email from external users using 

Set-DistributionGroup -Identity "Group Name" -RequireSenderAuthenticationEnabled $false

You must do two things for all these 15 distribution groups:

1. Check the option to receive mails from unauthorized receipients

2. Create transport rules, which will delete mails from all receipients to specific distribution group, with exception to specific domain.

But  i want also to receive internal mail on those groups. if transport rule rejects receiving from all recipients, then how we could be able to receive mails from All internal Users ?

BR//

Jubayer