Activesync broken after upgrade to iOS 10.2

Dear All,

I have an own Exchange 2010 server and all our iOS devices are configured for it. I have an iPhone 7, iPad Pro and iPad Pro 12.9.

Yesterday I upgraded my iPad Pro 12.9 to 10.2. The upgrade went well, but now my email refuse to synch with the server. It returns the message "Cannot get mail, the connection to the server failed". M iPhone 7 and the other iPad still on the previous iOS version are synching fine. What I did I also upgrade my iPhone 7 and iPad Pro to iOS 10.2. What happened then is the same problem. It cannot longer sync with my exchange account.

I tried a few things like reset network settings or disabling wireless on my iPhone 7 to be only on cellular. I also re-created the email account several times with no luck..

I had another old iPad around which has never setup my email account before. The iPad had still iOS 9 installed. So I was thinking maybe there is a problem with ActiveSync and installed my email onto this iPad. It worked straight away. Then I went ahead and upgraded this iPad to iOS 10.2 and now it stopped working too. With this iPad I did a full reset and deployed it as a new iPad again which has now iOS 10.2, but I was not able to verify my Exchange account.

My family has iPads and iPhones too, but not yet at level iOS 10.2 and they are all working.

I suspect Apple changed something in iOS 10.2 with the ActiveSync protocol which does not like my Exchange server anymore.

BTW: I have also an Android table and it works still fine with my Exchange email account.

Any hint is highly appreciated!

Thank you!