The weirdest thing is happening with our exchange, two weeks ago select users using iPhones cant connect to our exchange server using the email app on the iphone. Maybe 5 out of 200 users, and from what I've seen it's only on newer accounts. If you take that same user and use a 3rd part app like cloud magic, the user account works.
The only error we are getting is below:
Unable to send a notification for subscription GgB0cnMtZXhjaGFuZ2UucmlnaHRzdGVwLmNvbRAAAADdOyUwyza4Rb+f8gbks2PA. (Send attempts: 6)
The only change we've made was 3 weeks ago, remove a PDC, transferred roles and demoted the server. First thoughts are that is the cause of this, but everything is checking out.