The Set-EmailAddressPolicy cmdlet is needed for this.
Open the Exchange Management Shell and enter the following command:
This will show a list of Recipient Policies that are available in your Exchange organization. We can use this output by piping it into the Set-EmailAddressPolicy cmdlet:
Set-EmailAddressPolicy –IncludedRecipients AllRecipients
The Recipient Policies are now converted you can open them in the Exchange Management Console. Please note that the examples mentioned above are pretty simple policies. If you have more complex policies please test this thoroughly. If you have any Mailbox Manager policies, these have to be removed.