"Immediately after updating to iOS 4, users may notice that Exchange ActiveSync Mail, Contacts, or Calendars don't sync, or sync slowly. In addition, some Exchange Server admins may notice their servers running slowly," notify Apple via KBTS3398.
To resolve, users should install a configuration profile from Apple that increases the amount of time iOS 4 device will wait for Exchange Server to responds. For best results, profile should be installed on as many iOS 4 devices at your company as possible.
To install profile:
- Use Safari on your iOS 4 device to download configuration profile. It may be easiest to read this article with your iPhone or iPod touch and tap download link there, but you may also email attachment to another email account on your iOS 4 device, and tap attachment to open it
- Tap Install to install profile, and enter your passcode if prompted
- A warning message will appear because profile isn't signed. Tap Install Now
- Tap Done to complete installation, then power off your device and power it back on
- Wait for your Exchange data to finish syncing
After installation, the profile will be listed under Settings > General > Profile.