Apple has take note of an issue with iOS4 that can cause your Mobile Email or Exchange mailbox to be slow or even stop syncing entirely with your iPhone. They have recommended the following fix that installs a new configuration profile for users affected by the problem.
To install the profile:
- Use Safari on your iOS 4 device to download the configuration profile. It may be easiest to read this article with your iPhone or iPod touch and tap the download link there, but you may also email the attachment to another email account on your iOS 4 device, and tap the attachment to open it.
- Tap Install to install the profile, and enter your passcode if prompted.
- A warning message will appear because the profile is not signed. Tap Install Now.
- Tap Done to complete the 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.
See Apple’s support article for more details: http://support.apple.com/kb/TS3398