Version: 5.1.3
Linux Mint KDE 18

I have an uncapped adsl connection at home.
However, when I am on the road I use a 3G service.
This includes 2GB data cap per month.
If I exceed the cap, I get charged (automatically, with no warning, at R2/MB - imaging paying $2/MB or EUR2/MB or equivalent in you country).

After a umber of years of using Cinnamon, with Thunderbird I switched a week ago.

The system monitor shows the down/upload speeds, but not total data. So I run vnstat - but, 3G is so fast that I can get myself into real trouble financially before I am even aware.

How can I constrain this?
(For example, Thunderbird has an option to limit sync'ing to the last x-days.)

Ideally, I would want to do no sync'ing if on 3G.

I think this issue should be addressed somewhere else in the stack, I think. As far as I know, KMail only knows that it's online, or not. But it may be worthwhile to file a wishlist on bugs.kde.org.