Step 1 - Create an Exchange Mailbox to be used by Riva
Create a mailbox or use an existing service mailbox that Riva can use to connect to Exchange.
Step 2 - Grant Full Access Permissions in Rackspace
With hosted Exchange services, the Riva connection account should be an administrator level account that is granted "Delegate" full access permissions to each target user. Here are the steps in Rackspace:
Login into the Rackspace Management console as the company Rackspace account.
Choose to manage Email Accounts.
Select a target user's mailbox.
In the "Mailbox Details" under the "General" tab, ensure that the options Visible in the Exchange Global Access List and Public folder admin are selected.
Under "Permissions", type in the email address of the Riva connection account, ensure that the "Full Access" permissions is assigned and click the Add button.
Confirm that the Riva connection account has been added with Full Access" permissions assigned and click Save.
Repeat steps 3 to 6 for the rest of the Exchange target user mailboxes.