I’ve been working on an Exchange 2003 to 2007 migration this week and have run across an issue I hadn’t seen (nor really heard of) before!! A Citrix Application Firewall, version 5.5.6, was being used to “front-end” the Exchange 2003 environment. When switching the firewall to work with the Exchange 2007 CAS, OWA worked ok but ActiveSync sure didn’t. When trying to synchronize, the mobile devices would fail with the support code “0x80820001” (most of the time) or would state that they had sync’d but not actually display any messages, calendar appointments, or contacts.

Try a Google search for “ActiveSync” and “80820001”. You won’t find much, nor will you find anything here:


ActiveSync connectivity was fixed by changing the “Allowed Request Headers” setting on the Application Firewall.

1. The Security Policy was edited at the Site level.
2. Inside the security policy, select Input Validation.
3. For the option “Define Allowed Request Headers”, select “Allow All”
4. Save the configuration

Once this was completed, ActiveSync worked! The firewall administrator here is going to research the request headers required for ActiveSync. Once the specific request headers for ActiveSync are identified, the Allowed Request Headers value will be set back to “Custom”.