White screen @ iPhone mail iOS11.2.5

Hi, after upgrading my iPhone 6SPlus ro iOS 11.2.5 I cannot use my mail app anymore. When I push it, it opens for a split second, the screen becomes white and I am back to the home screen. I have tried various things including restoring to factory settings and restoring from backup, and installing as a new iPhone. Nothing helps. If I install a 3rd party mail client, that works, just not the Apple mail itself. Any ideas?

Thanks so much, EF