Exchange 2013 SP1.
We have to exchange information with external users in the Internet. Addresses of those recipients are created in our Exchange organization as mail contacts. About 30 distribution groups containing those contacts are created in the Exchange organization as well. Our users are able to successfully send messages to the external users using those distribution lists.
Our users need to sort incoming replies and put them to different folders basing on the distribution group memgership. If the sender is a malbox inside the organization, it's simple. We just create an Inbox rule which checks the sender's group membership and moves the message to an appropriate folder. However, it doesn't work if the sender is outside the organization, even if there is a mail contact corresponding to the external sender's e-mail address.
The department in question has several hundred external users sending messages from the Internet, so sorting the messages manually is a difficult task. The department's users have to find out to what distribution group the sender's address belongs, and only then move it to an appropriate folder. Is there a way to automate this procedure?