I excluded WhatsApp from the VPN. Problem solved.
Thanks for your additional info.
Of course, you need online connection for WhatsApp: that is clear
in WhatsApp on Android 7.0
Comment by StockTrader
the VPN is ON all the time, the emails are working perfectly in and out.
The option iVPN ALWAYS ON is set OFF by default in the Android 7,0 system.
Marco - StockTrader