An option to archive emails without attachments

As a web-hosting reseller, I would like an option to archive emails without attachments, so that some clients that prefer to save emails forever we can save disk space.

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I'm noticing one of my clients sends and receives images and documents to their customers, and with those images usually being around 7MB, disk space usage is very high.

The client is interested in keeping emails archived so they can dig up an email if there is a disagreement/conflit with their customers and they need to prove what was agreed upon. The images are not required in this situation.