Datacenters don't spin down drives. Like ever. Spin up time is too much overhead when a request finally comes in.

The "savings" here is that removing data from the mail hosts in general means that less drives need to be brought online to handle new data. Less drives overall = less wattage.

The better request would be to go onto icloud and delete all those pocket pictures... or duplicate pictures that you uploaded. One picture can be dozens if not hundreds of text emails.

I run most of my own services including email... My inbox with stuff from 2006/2007 time-frame and about 150,000 emails is a mere 11.6GiB... My automatic image backup folder on Nextcloud eclipses that readily for just one month of images/videos (I have kids).