This one caught me out recently. Scenario:
All http://officecdn.microsoft.com is whitelisted and available, definitely no issue there.
- All other updates seem to come down fine.
- There are no ADR rules at all in place.
- Running a full sync produces the error below:
My client downloads updates through a proxy server and naturally the correct details for the proxy were in place on the Site System Settings under Site System Roles. Also the checkbox for Use a proxy server when synchronizing software updates was checked under the Proxy And Account Settings tab under the Software Update Point Properties role.
Despite the fact that ADRs were NOT created or used in any way, it transpired that the checkbox Use a proxy server when downloading content by using automatic deployment rules also had to be checked. Once this was selected, O365 updates started syncing.