Reply / Forward Mail Errors with iOS11 on Exchange ActiveSync in SmarterMail

With Apple announcing of iOS11 for the new line up of their iPhone 8, iPhone X, it’s pretty an exciting news. As iOS11 is rolling out beginning of Sept 19 2017, one of the drawback that’s going to hit is on the mail server environment particularly on the Windows Server 2016 running on Exchange ActiveSync (including both Microsoft Exchange and SmarterMail as well as other mail server that support ActiveSync).

The major issues with the iOS11 is that Exchange ActiveSync (EAS) users will not be able to REPLY to, or FORWARD, messages with attachments from the default Mail app on iOS 11. Please understand that 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

Again, this is ONLY necessary if your mail server is running Windows Server 2016. NOTE: Editing the registry should be handled by someone with experience. Do reach out to your server admin or hosting provider for help if you are not experience to do this.

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