Exchange ActiveSync fails on iPhone after upgrade to iOS4

I’ve spent a fair bit of time today trying to sort out my iPhone sync to my Exchange Server, failing miserably. It used to work, pre-upgrade to iOS4, but for some reason fails to sync.

Symptoms were:

• iPhone fails to sync, generic timeout error (or is very slow)
• https://www.testexchangeconnectivity.com/ successfully tests the mailbox access

The server was configured as per http://support.microsoft.com/kb/817379/en-us to allow OWA/ActiveSync with SSL on OWA.

The iPhone was configured to accept the SSL certificate on the Exchange Server.

My brother Tom sent me this Apple KB (http://support.apple.com/kb/TS3398) which he’d found from the other side – Exchange servers he was managing were under very heavy load, which is another symptom of this issue.

I installed the new configuration as per the article, restarted the phone and the issue was fixed!