What to do anout "Set the server's HBI to 59 minutes"
In this page https://support.apple.com/en-us/HT203719 Apple descripe, that the "Exchange servers HBI is to be set to 59 minutes."
Apple then links to a Microsoft artikle that says that HBI is to be set to a interval 1 minute an 45 minutes.
What to do now???
It applies to any iOs device iPhone/iPad, using standard mail and calendar app.
iPhone 6, iOS 9.3.2, Mail/Calendar