Does your organization have a email list that users keep using for personal notifications to the company?
A good way to prevent all the internal spam is to setup message moderation
Moderation will notify the moderator when a message is sent to the moderated distribution list. the moderator will have the ability to approve the message or deny the message.
You can specify what users have automatically have approval. To do this:
Open the Exchange Management Console
Open Recipient Configuration
Select Distribution Group. Open the properties of the Distribution Group you want to moderate. Select the Mail Flow Settings Tab
Select Message Moderation and then properties
Specify the users that can approve messages. Specify any users that are exempt from the moderation’s. Also, specify user notification settings
Select OK and apply when you’re done.