Securing Exchange emails to a single account

In other words, if an email was sent to user1@mydomain.com, replies can be made from user1@mydomain only, and all attempts to communicate from other accounts in mydomain.com fail with ndr.

By default only user1 has permission to reply any email send to user1@mydomain.com since user1 has permission on his own mailbox.

There is circumstances especially the reply mailbox is a shared mailbox and other has permssion such as send on behalf. Other user able to reply on behalf on shared mailbox, where the From: will be the person who has send on behalf of shared mailbox

I should be a bit more specific, and I apologize for not providing this info first.

Each of the users at this client monitors their own account and a shared account.  What we want to limit is the ability of any of the users to email from their own corporate mailbox someone who initially sent an email to the shared account, thereby allowing only a response or direct correspondence from the shared account only.  

Hope this cleared it up.

Thanks for the quick reply.

So I figured out how to prevent users from sending to specific email addresses based on transport rules and distribution groups.

The last item would be to automatically populate a dynamic distribution group with sender's email addresses based on emails coming in to a specific email address within mydomain.com.

Can this be done?

Thanks,

Well it possibly could, but it isn't something I would advise.

To be a member of a group requires an AD object. For external senders to be a member of a group requires being a contact. Therefore you would have to get the email address, create the contact then add them to the group.

The contact would then be used by anyone sending OR receiving email involving that address. Unless scripted correctly it would appear in the GAL.

The group would get very large very quickly and that would have a detrimental effect on the performance of your Active Directory domain and email flow.

EVERY email that is sent by your org would have to be checked against that list. That means the distribution group being expanded every time an email is sent. The load on the domain controller would be huge and it would cause your email processing to slow down considerably.

I stress what I have said above - this is a VERY VERY bad idea and I would strongly discourage you from trying to find a solution. Go back to whatever PHB requested it, and tell them it cannot be done and to manage their staff rather than getting IT to do it for them.

Simon.

Understood.  Thank you very much for the assistance.

I've requested that this question be deleted for the following reason:

very old