I am seeing this event viewer item several times each day on my Exchange 2010 SP3 CAS servers. The CAS servers (3) are sitting behind an F5 Big IP load balancer. The SSL cert is on the F5 VIP. There is no firewall active on any of the CAS servers.
Activesync is working fine. Smartphones are syncing fine. I'm just curious if there is a way to stop this error in the event viewer.
Log Name: Application
Source: MSExchange ActiveSync
Date: 9/20/2016 7:38:43 AM
Event ID: 1100
Task Category: Requests
Exchange ActiveSync device requests for your users are being blocked. This problem frequently occurs when the HTTP OPTIONS method request isn't allowed by the firewall. Please check the firewall that filters requests in front of your Client Access server and the Microsoft-Server-ActiveSync virtual directory.