Hi CEklx,
I believe it really comes down to the question on if this customer wishes to keep these emails in the system.
An evaluation on what and how much storage is being consumed by these emails would provide more insights on the necessity of keeping these records (or moving to any other data location if business permits).
For example, if a lot of file storage is being used because these emails contain by default large attachments, that customer might consider adapting the content according to their limitation requirements.