There is an unresolved compatibility issue with iOS 11, which will be released by Apple to the public tomorrow, and Windows Server 2016 that affects all versions of SmarterMail, as well as other mail servers and services, including Microsoft Exchange Server.
What’s the issue?
Exchange Active Sync (EAS) users will not be able to reply to, or forward messages with attachments from the default Mail app on iOS 11.
What’s the cause?
The cause of the issue is related to the implementation of HTTP/2 in either Windows Server 2016, or in iOS11. Apple is now using HTTP/2 with iOS because Windows Server 2016 supports it, instead of the more legacy HTTP/1.1.
If your mail server is running an older version of Windows Server, iOS 11 will continue to use HTTP/1.1, and this is not a problem.
What’s the workaround?
System admins can modify the Windows Server 2016 registry to act as older versions Windows Server, and fool iOS 11 into using the HTTP/1.1 protocol. The following keys would need to modified: (and the server rebooted)
EnableHTTP2Tls REG_DWORD 0 — the default is 1
EnableHttp2Cleartext REG_DWORD 0 — again, the default is 1
Remember, this is only necessary if your mail server is running Windows Server 2016.