Mail constantly 'saving drafts'

Hi

I have an issue with my Apple Mail app on my Retina Macbook Pro. At the bottom left corner where the current activity gets advertised, it constantly says 'Saving 1 of 100 Drafts' with a slightly greyed out Number at the bottom (3.29 GB).

I've tried a rebuild and also deactivated and reactivated my icloud Mail, but nothing helps. In my actual drafts folder in the Mail app there are no drafts at all. Same on my iOS devices and on iCloud.com.

Where can I find these 3.29 GB worth of drafts on my Mac?

I'm not sure if this is also a part of the problem: Whatever I do on my Mac in the Mail app it isn't synced to iCloud nor to any of my iOS devices. Here too: Deactivating and Reactivating the Account does not work.

I somehow think that constant 'Saving 1 of 100 Drafts' is blocking everything.

Cheers

Steve