Excess Cellular data usage: Mail uses too much data when retrieving mail

The data usage on my iPhone 5S started skyrocketing with iOS 8.3. At first it was because podcast apps were not honoring the "do not use cellular" setting and downloading over cellular network anyway.

That problem got fixed with iOS 8.4.

The problem I now have is that fetching email from 4 email accounts consumes anywhere from 1 to 5 megabytes, even if there is no new email!!!!

I have disabled the autoloading of images in emails, but that hasn't helped much. I have turned off app background refresh for just about all apps, but that hasn't helped.

I use DataWiz app to monitor data usage, and simply checking email will cause anywhere from 1 to 10 megabytes of usage, usually for retrieving as many as 10 emails.

All accounts except for iCloud are configured to use IMAP with SSL. In addition to iCloud, I have a gmail account and two privately hosted email accounts.

Checking email did NOT consume this much bandwidth before iOS 8.3, nor should it! Is there a setting I am overlooking?

I get the impression this excess data usage results from a bug that forces the iPhone to fetch email messages over and over again. I have 19 gigabytes of free space on the device, so this should not be happening! I have plenty of space for all the email.

Thanks in advance.