Exchange ActiveSync issue on Windows Server 2016 with iOS11

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Exchange ActiveSync issue on Windows Server 2016 with iOS11

Exchange ActiveSync (EAS) users will not be able to REPLY to, or FORWARD, messages with attachments from the default Mail app on iOS 11. This is NOT a SmarterMail issue but an iOS 11 and Windows Server 2016 compatibility issue that affects ALL versions of SmarterMail as well as other mail servers and services, including Microsoft Exchange Server customers using Windows Server 2016.

The cause of the issue is related to the implementation of HTTP/2 in either Windows Server 2016 or in iOS 11. HTTP/2 is a major revision of the HTTP network protocol used for communication across the internet. Windows Server 2016 and Windows 10 both implement, and default to, HTTP/2 versus the more legacy HTTP/1.1. With iOS 11, Apple is now using HTTP/2 because Windows Server 2016 supports it.

If your mail server is running and older version of Windows Server, you will not see this problem as iOS 11 will continue to use HTTP/1.1.


As a workaround, system administrators can modify the Windows Server 2016 registry to “act as” previous versions of Windows Server, essentially telling iOS 11 to use the HTTP/1.1 protocol.

The following keys would need to be modified AND the server rebooted:


EnableHTTP2Tls REG_DWORD 0 — the default is 1

EnableHttp2Cleartext REG_DWORD 0 — again, the default is 1