Upgrade the default Email Address Policy to Exchange Server 2007 OPath format using this Exchange Management Shell command.

[PS] C:\> Set-EmailAddressPolicy "Default Policy" -IncludedRecipients AllRecipients

If you have any additional custom EAPs you can upgrade them by following the advice at the Set-EmailAddressPolicy Technet page.

In organisations with only the default Email Address Policy, Address Lists, and Global Address List, you can complete the Exchange upgrade with a script instead of running each command manually.
Download the Exchange Transition Script.