If I use one email account to confirm/open the Purchase Order (PO), am I able to issue the invoice using another email account?

Yes, but only if these two email accounts are tagged to the same Ariba account.

The Ariba account that can view the PO will also be able to access the “Create Invoice” button to submit the invoice. The system administrator of the Ariba account can do the following:

• Add new users/email accounts that can access the Ariba account.
• Add roles to existing users/email accounts to allow submission of invoice.

Please refer to the user guide on “Adding Roles, Create New User & Make A User as the Administrator”.