Mail takes up much more storage than it should.

I've been using WhatsApp on my computer for a while but even now do I sometimes need to mail certain large files to myself so that I can download them on my computer and delete them from my iPhone. Thing is, even if I use MailDrop to send download links instead of attaching the large files themselves, all that happens is Mail taking up the storage space saved by deleting the copy of the file received in the WhatsApp chat, which results in no overall gain. Mail is now taking up over 5.35 GB, and the files never get deleted even when the 1 month to download the files expires. So why does Mail keep a local copy of every file I send via MailDrop? Is MailDrop not intended for the exact opposite: to facilitate access to uploaded/hosted files for 30 days without having to keep them on one's device? Now I have to consider uninstalling and reinstalling Mail, which will irritatingly require me to add and configure all my 5 accounts again.
* Update: Mail is now taking up over 5.5 GB. Should I consider pushing harder for a Guinness record? I only have 64 gigs though, much of which is already reserved for the operating system itself, so it won't be long before someone having a 256-GB device beats me. Plus, I will have lost all my important data so that I can have all the available storage taken up by Mail so as to break that record.