When an email gets stored in CRM it is an independent copy of what is stored in a user's mailbox - this not effected by anything on the Exchange side. In an out of the box scenario there is nothing to purge or archive old data. The assumption being
a person could always go back through custom history and find all the communication.
You can control the maximum size of files in CRM - this could potentially help extend the length of time before you run into issues. You could look into the native SharePoint integration and maintain the attachments there or a different file storage location.
There are some solutions floating around that can do this.
Jason Lattimer
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